Ambiguous area of bistatic SAR will vary with the change of bistatic geometrical configuration and is difficult to be predetermined. Ambiguous scattering points in the scene can be found through observing the momentary image grid formed by iso-range contours and iso-Doppler contours, but it is an attended method which is invalid in many unattended occasions. In the paper the problem has been converted into an unconstrained nonlinear optimization, the idea of random search is combined with Nelder-Mead method and a simplex-based approach to seek ambiguous scattering points has been presented. Simulation results demonstrate the validity of simplex-based approach. (4 pages)