Buddhism thoughts did not form and establish at the moment when Buddha had taught, but with the passing time and the change of the space, the thoughts evolved continuously. Because Buddhism is a practical religion which could not forbid the influences form the living culture and made the necessary changes. In this paper, the author wants to probe into several basic questions hidden in Mahayana Buddha dharma, such as: Th establish time? The happened place? The reason to happen? And how to happen? Though to answer these questions correctly, it is really impossible. Because India does not have enough historical records, so there are really few reliable believable historical data, and because the name of the Mahayana Sutra's writers used to use the name of Buddha or Bodhisattva, therefore it's even more difficult to find out the answer. But as this is the worthy work to do, so I won't give up tracing to the source, hope at the end of the paper can find out a accepted and received result.
