Aiming at situation that small unmanned helicopter（SUH）changes its attitude during landing stage

and non-differential GPS lacks of precision

a monocular vision-based SUH height measurement method is researched to enhance the quality of autonomous landing.Under the condition of obtaining the body attitude angles previously

recognizes and extracts the parallel feature straight lines according to on-board camera projection model

real-time calculate height during landing.The feasibility of this method is testified on the measuring system

and experimental results indicate that the method performs a relative high feature recognizing rate and real-time and accuracy of output result can entirely meet requirements of landing when tilt angle exists between airframe plane and landing plane.