Compared to monostatic SAR, BiSAR brings lots of benefits. However, because the transmitter and receiver are put on different platforms, synchronization errors are generally introduced into the received data in real bistatic systems. Additionally, the position of the transmitter would affect the quality of traditional synchronization and imaging algorithms. Considering the situations above, an imaging algorithm based on entropy optimization and direct signal with nonsynchronous echo directly is proposed. It could avoid complex mathematical modeling analysis and could get accurate position of transmitter. First, the synchronization errors are eliminated through matching echo signal with the direct signal. Second, extract the phase of direct signal and calculate the range between the transmitter and receiver. Then search the accurate imaging parameters based on entropy optimization. After that the image could be well focused.