The so-called nominalizer zhi, the function of which is still debatable, refers to a particle placed between subject and predicate forming a subordinate or embedded clause in the Pre-Qin period. It was known to be used frequently in the Pre-Qin period, but disappeared later in the stream of history. In this research, we investigated zhi from perspectives as follows: the distinction between the nominalizer zhi and other particles zhi, the grammatical function of zhi, the conditions on zhi’s deletion, and the process and mechanisms of zhi’s decline. The main conclusion is that the frequency of zhi decreased remarkably in the late Warring States period, and fell violently in the Western Han Dynasty. Through investigation on narrative documents of Old Chinese, we believe that the zhi in embedded clause could have been withdrawn from the colloquial language in the Western Han Dynasty. Another observation in this paper is that two motivations originally existed in the Pre-Qin period which may be responsible for zhi’s decline: the first is that zhi is arbitrary under certain conditions; the second is that zhi is functionally deficient. The former says that the conditions for zhi’s deletion, which were complex in the Pre-Qin period, were difficult for the people in the Western Han Dynasty to grasp when the construction of the language was in a state of fluctuation, subsequently, the rule was re-analyzed, and zhi was more easily to be deleted; the latter says that zhi's functional ambiguity, the functions of which correspond to functions of several conjunctions, together with its inability of nominalizing a clause without the appearance of a subject, make a good reason for zhi to give way to other conjunctions.