In order to get the accurate depth of shallow water in a lidar bathymetry, it requires to measure the distance between sea surface and bottom,and the distance between airplane to sea surface. It is very helpful for the post-data process to get the mean ocean surface and the wave height. A high resolution time interval module is developed to get the high accurate distance between airplane to sea surface. The module is based on ASIC TDC chip with the technique of the delay-line interpolation. The module has two channels with a resolution as high as 250 ps, respectively. The hardware and software of the module and the testing results are presented.