Lidar can accurately and quickly obtain the three-dimensional(3D) spatial information of the target, which is a commonly used high-resolution imaging technology. Combined with high frequency pulse laser, streak camera and signal processing technology, a 3D imaging system of lidar is designed in this paper. Among them, the pulsed laser has the characteristics of high peak power, which can effectively detect long-distance targets. Compared with high frequency microwave modulated laser pulse, high energy laser pulses can be obtained by combining pulse compression and Fabry-Perot oscillation cavity. The streak camera is a kind of high-speed camera with the ability of fast weak light detection, which can detect long-distance targets. Mean filter and neighborhood mean filter are used to suppress the background noise of streak camera. Band pass filter and matched filter are used to suppress low-frequency noise and increase signal-to-noise ratio. According to the intensity distribution of noise, threshold filter is used to filter the residual noise, and finally high-precision 3D target image is obtained. The experimental results of 3D target imaging in air and smoke show that the system has high range resolution and strong ability to capture target details.