We estimated the influence to perceived depth by spatial-frequency modulation difference between front and rear images in DFD (Depth-fused 3D) display. Perceived depth in DFD display can be expanded by low spatial-frequency modulation. In this paper, perceived depth influence by difference in frequency modulations of front and rear images is estimated. Wide difference in frequency modulations degrades perceived depth to discrete depths at front or rear planes. On the other hand, small difference in frequency modulations results in continuous and linear perceived depth.