System size is of great concern when the laser ranging system is put into practical usage. A multi-pulse gain-modulated three-dimensional imaging system is presented,which uses low pulse energy laser as illumination source. By utilizing multi pulse accumulation method,a 5-μJ pulse laser source was used to achieve a detection range of 100 m with light fog and range accuracy greater than 3 m during indoor experiment . With the using of low pulse laser source the system size is greatly reduced.