The invention discloses a low-spatial-domain collision avoidance system and method for an unmanned aerial vehicle. The method comprises: a flight data recording module collects unmanned aerial vehicle flight information and a wireless data transmission module transmits related data of flight information of the unmanned aerial vehicle to a ground unmanned aerial vehicle monitoring system, thereby calculating a flight path of the unmanned aerial vehicle; and the ground unmanned aerial vehicle monitoring system carries out unmanned aerial vehicle flight information data processing by using a collision avoidance algorithm and informs an unmanned aerial vehicle operator of state information of the unmanned aerial vehicle in real time. According to the invention, three-dimensional spatial Cartesian coordinates of all unmanned aerial vehicles are measured by a GPS; fitting of flight paths of the unmanned aerial vehicles within a current period is carried out based on a cubic spline curve fitting method; whether a closest distance of flight path curves between the unmanned aerial vehicles is smaller than a security distance is calculated to determine whether a collision will occur; and flight operators of the unmanned aerial vehicles are informed of a collision result timely to change flight directions and speeds of the unmanned aerial vehicles timely.