A gradient descent algorithm with adjustable parameter for attitude estimation is developed ,aiming at the attitude measurement for small unmanned aerial vehicle (UAV) in real-time flight conditions .The accelerome-ter and magnetometer are introduced to construct an error equation with the gyros ,thus the drifting characteristics of gyroscope can be compensated by solving the error equation utilized by the gradient descent algorithm .Perform-ance of the presented algorithm is evaluated using a self-proposed micro-electro-mechanical system (MEMS) based attitude heading reference system which is mounted on a tri-axis ttable .The on-ground ,ttable and flight ex-periments indicate that the estimation attitude has a good accuracy .Also ,the presented system is compared with an open-source flight control system which runs extended Kalman filter (EKF) ,and the results show that the atti-tude control system using the gradient descent method can estimate the attitudes for UAV effectively .