In order to reduce the effects of parameter variations and complex environment disturbances on the altitude control of parawing UAVs (unmanned aerial vehicles), an altitude control strategy based on LADRC (linear active disturbance rejection control) was studied. An eight degree of freedom model of a parawing UAV was built, and the wind and rain models were introduced for the accurate simulation of real flight environments. Based on the features of LADRC, the whole control structure was determined. As a result, the internal and external disturbances were estimated by using linear extended state observer and compensated real-timely by the feedback control law. Flight simulation experiments under various disturbance conditions were conducted. Simulation results show that the altitude control method based on LADRC can not only accurately estimate and compensate the internal/external disturbances but also implement precise altitude control. Compared with standard PID controller, the LADRC controller has better robustness and disturbance rejection ability.