Abstract: Arc array Bistatic synthetic aperture radar（AA-BiSAR）is a novel imaging system for full azimuth observation, which can obtain high data acquisition efficiency and reduce vulnerability of arc-array monostatic SAR. Due to the arc antenna configuration of AA-BiSAR, it is difficult to have access to the two-dimensional frequency spectrum for AA-BiSAR via the principle of stationary phase（POSP）. In view of the above problems, the method of implicit function is introduced into AA-BiSAR. The stationary phase can be considered as an implicit function of the Doppler frequency, and after deriving the implicit function equation, the stationary point can be solved by algebraic operation Thus, the 2-D spectrum can be directly obtained by using the principle of stationary phase. In this paper, an imaging algorithm based on the derived spectrum is developed for AA-BiSAR. The numerical simulation results of point target demonstrate the validity and effectiveness of the approach.