By the purpose of ensuring the precision positioning when the unmanned aerial vehicle (UAV) flies at a low altitude and the safe landing when it is in approaching, a fast and precise laser altimeter with lightweight and low power consumption is developed. Based on the principle of pulsed laser ranging technique, adopted continuous wave with the features of high precision and fast testing, integrated signal processing, computer-controlled simulation, virtual prototyping, precision machinery, precision optics and other advanced technology, the design and development of the device are completed by utilizing the virtue of infrared semiconductor laser, special ranging sensor module, high-speed A / D converter and high-performance SCM etc. In the experimental stage, hardware-in-the-loop simulation technology is flexibly used to avoid the complexity and error of computer modeling and simulation. The test results of the experiment show that all the technical characteristics meet the requirements of unmanned aircraft altimeter system, and the low-flying UAV can be exactly located and can safely land by using the system in the general environment.