hi I'm new and i have a question
when did the chinese start to use "special units" or professional warriors
you know those special kind of warriors who could take on a whole lot more.
one more which dynasty had the most cavalary or the best(and the yuan dynasty doesn't count 
)
I see two parts to your question:
1. When did the Chinese start to use "special units," which are special forces?
2. When did the Chinese start to employ professional warriors, which are full-time soldiers who do not farm (except under the Fubing system) and earn pay?
I do not know the answer to the first one, but I can guess that the military elite consisted mainly of the aristocracy.
Professional soldiers, in small amounts, existed even during the Zhou Dynasty, though the backbone of the army was its
chariots. Professional amies became massive during the Warring States period and remained large throughout imperial China. Professional soldiers were prevalant in China for several reasons:
1. China had a relatively short period that resembled feudalism--Pre-Warring States.
2. China has had a traditionally dense population and could afford to deploy larger armies.
I'm not sure if standing armies, e.g. professional soldiers, existed during the Shang Dynasty.
General Zhaoyun discusses Chinese military history
here, as does
Snowybeagle, and there's a thread discussing Warring States military
here.
Finally, here's a
thread that discusses Chinese feudalism, a hereditary warring class, professional armies and more. From that thread:
as we all should know, during Xia, Shang and Western zhou, the nobility were the warriors. period.and by Eastern Zhou you had knights called 士(japanese use this character to occasionally denote Samurai). The Warring states era changed this by introducing large conscripts to augment the professional Shi
but thats pre-Imperial China and we're focusing on Imperial China.
the existence and importance of a professional warrior "class" during Imperial China came and went and changed constantly. This is compounded by the difficulty of labelling a "class" in Imperial China when class systems were no longer rigid.
i am simply arguing that the difficult skills that would be tested in a Chinese military examination such as standing archery, horseback archery, cavalry lance/sword techniques, weight lifting,etc,etc would only be passed by people who were career warriors. There is absolutely no reason to believe that Chinese cavalryman were of poor quality EXCEPT in certain periods of stagnation. These periods of stagnation in quality can also be said of Khitan warriors during the late days of Liao.
Here are some examples throghout Imperial China reflecting the fluxating concepts of professional warriorhood
-by the reign of Han Wu Di, he clearly saw that large conscripted peasent armies were ineffective against the Xiong Nu. He made cavalry the main striking force of the Imperial Army smaller in number but higher in quality. This created as David A. Graff puts it, a semi professional army of the Han dynasty IE life long career soldiers
-During the Sixteen kingdoms era, Ran Min's forces were small (all Han Chinese) yet clearly they were professionals seeing as they were able to defeat large nomad armies several times their size
-During the Tang dynasty, most campaigns rarely had over 10,000 men and clearly did not rely on semi-trained peasent conscripts. As we also know, by the end of the Tang, the country was run by warlords (professional warriors)
even as late as the Ming dynasty, military positions were hereditary(this particular system inherited from the Yuan dynasty). the government gave tracts of land to these warriors so they could make a living in times of peace but they were expected to train their skills constsantly. General Qi was NOT just any officer. He inherited his position from his father. While this system was obivously not as static as feudal Japan's, the children of high ranking military officers were bound to their father's position. Stephen Selby goes in depth in his book Chinese archery regarding this.
