‘Zheng’ used before the verb to show progressing meaning is not efficient to form a independent sentence, it is possible to use the state verb and semelfactive verb in the progressing sentences, and it can also used with the auxiliary verbs to show imminent situation. According to these points, this paper tries to confirm whether ‘zheng’ has the function of indicating the progressing aspect through the comparing with ‘zai’. ‘Zai’ fulfills all the basic semantic elements of progressing. That is the agent is in the middle of spatial orientation at a given time of doing something. But ‘zheng’ only fulfills the standard of a given time and satisfies other standard sometimes or can not satisfies them all. ‘Zheng’ can express the progressing aspect at a quite limited degree, because it can be explained that it is the extension of the original meaning of ‘be straight not leaning’. There is long process for ‘zheng’ to become the real aspect marker after the grammaticalization. In addition, it is appropriate to consider ‘zhengzai’ as the combination of ‘zai’ and ‘zheng’ which shows the coincidence in time.