The invention discloses a laser-range-finding-based UAV landform detection system, so that problems of slow detection speed, weak anti-interference capability, and poor measurement precision in a severe environment in the prior art can be solved. The detection system fixed at a UAV by a motor capable of rotating back and forth in a range of from 45 degrees to 90 degrees comprises an ultra-high-speed laser transmission module, a light speed processing circuit, a high-speed digital signal processing chip, an ultra-high gain laser receiving module, a precise optical module group, and a motor control circuit. The high-speed digital signal processing chip provided with a light source output driving terminal is used for generating a narrow pulse signal emitted by laser, calculating a laser flight time difference and determining a detected ground landform state; the ultra-high gain laser receiving module is used for receiving a laser echo; and the motor control circuit is used for controlling a motor to rotate back and forth in a range of from 45 degrees to 90 degrees. The detection system has advantages of simple structure, scientific and reasonable design, convenient usage, fast detection speed in a severe environment, high anti-interference capability, and high measuring precision.