A high-speed data acquisition and preprocessing system was proposed based on FPGA for echo signal sampling of laser radar. By use of embedded DRAM and synchronous finite state-machine, the designed system, triggered by a 1 kHz excitation signal, can sample the signal at the rate of 20 MHz, and the 4 096 sampled data can be accumulated correspondingly more than 5 000 times for the purpose of filtering background noise. The completed system was applied in a Mie scattering laser radar, which can achieve the spatial and temporal resolution of 7.5 meter and the detection range of 30 km.