Simulated synthetic appertnre radar (SAR) data films frtce from error of the SAR operation, but there still are aberrations introduced by the both film thickness variations and Simulated apparatus. In this paper we present a method that wavefront aberrations of simulated SAR data film can be measured by Mach-Zehnder interferometer. The method can be used separately for measuring the wavefront aberrations introduced by two different reasons. The wavefront aberration introduced by the film thickness variations is measured as compared the wavefront through, the iilin with the reference plane wavefront. And as compared separately the diffraction wavefront from the film with iwo reference spherical Avavefronts of different radii we obfciiined separately the azirmith wavefront aberration and the range wavefront aberration introduced by the simulated apparatus. In this paper some experimental results and analyses are presented. The method is also suitable for measuring wavefront aberrations of true SAR data film. The wavefront aberration introdaeed by the film thiokneSv9 variations may be Temoved by a liqnid gate. A tolerance of the wayefront abexrrtion introduced by the film thickness variations is deduced from the Rayleish criterion. From the tolerance we can judge whether or not the liquid gate is necessary.