Laser scanner, an important component of airborne LiDAR system, consists of several functional modules, and these function and module design methods were completely introduced in details. In order to reduce the weight and size of laser scanner, a novel four-size prism was proposed as the scanning component, the relationship of detecting distance and optical aperture was discussed, furthermore, the optical module was designed based on the parameter of detector. As the light source, a fiber laser had been applied to reduce the cubage, power and weight of the scanner, and then a collimator was designed for beam shaping. The results of the performance tests revealed that the scanner accuracy was 5 mm in 16 m range testing, and in 293 m range testing, the accuracy was 18 mm. The laser scanner was used in flight perform experiments as a part of airborne LiDAR system, the results from different flight altitudes were presented at the end.