Basing on the measurement of pulse time-of-flight, 3D imaging LADAR have ability to obtain the profile of target surface. As the convolution results of impulse response function of footprint and probe pulse, the reflected pulse will distort if the footprint contain a variety of distances. After discriminate process, this distort brings in a time error for distance measurement, which becomes the anamorphose on system imaging further more. According to the discussion of time-dependent scattering cross section, this kind of anamorphose is mainly decided by the slope of target surface when the system parameters and target distance are determined. A compensation method for height error based on detected slope has been put forward. First of all, the slope distribution of detected surface could be calculated from the point cloud data by two-way difference method. Then, the approximate compensation height error will be obtained, according to the slope-error relationship by assuming that each footprint be a tilting plane. After adding to the detected data, the first approximate target surface data has been acquired. The compensation result will approaching the real value by repeating the three steps above. As an example, simulation analysis of Gaussian pulse imaging detection has been given. The result shows that this compensation method is effective and efficient.