The invention discloses an unmanned aerial vehicle bridge floor coverage motion planning method, belongs to the technical field of unmanned aerial vehicle control, and aims to solve the motion planning problem that an unmanned aerial vehicle stably completes the full coverage of the bridge floor and meets the coverage resolution requirement in an automatic detection task of a bridge surface. The method comprises the following steps of firstly, establishing a geographic coordinate system, an airframe coordinate system and a bridge floor coordinate system, giving a measurement model of an airborne camera, and giving the definitions of a coverage space, a coverage surface and the coverage resolution; secondly, decomposing a topological structure of the bridge floor by adopting a linear scanning form, and determining a bow-shaped coverage path for each decomposition unit; then determining the coverage sequence of the units by adopting an integer optimization method; then giving two mathematical descriptions of the flight space of the unmanned aerial vehicle under a coverage task by combining the distance range from the unmanned aerial vehicle to the bridge floor; and finally, taking the flight stability of the unmanned aerial vehicle as an index, and combining with limitations, such as position, speed, acceleration, flight space, full coverage requirements, etc., providing a method for obtaining a motion trail function by adopting curve optimization. The method is suitable for the unmanned aerial vehicle to quickly and stably complete the movement track planning of full coverage of the bridge floor under a bridge detection task.