Abstract: Causative type unmarked patient prepositional sentence contains two statements, and there is a cause and effect relationship between them, among which the result is the main event and the cause is the minor event.The statement focus is expressed by the main event.For a causative type unmarked patient prepositional sentence, the resulting source component acts as a noun referring to things, which metaphorize the cause event in complex events, and whose meaning of causing results from the ancient Chinese make-acting.Causative type unmarked patient prepositional sentence can be transformed into the "ba" sentence, because the patient agent in such a sentence has the nature of the object.The circumstances for subject and object position exchange are inconsistent, the reason of which needs further study.