For wavefront sensorless adaptive optics systems,a control technique based on the orthogonal mode perturbance gradient descent (OP_GD) algorithm is proposed.The feasibility and convergence speed of this method are analyzed comparing with the serial gradient descent algorithm and stochastic parallel gradient descent (SPGD)algorithm.After that,an adaptive optics setup with liquid crystal spatial light modulator (LC_SLM) is set up,and the convergence characteristic is analyzed experimentally.The results show that this algorithm has a good global convergence characteristic and almost the same convergence speed as SPGD algorithm.However,compared with SPGD algorithm,the orthogonal mode perturbance gradient descent algorithm is easier to perform with hardware because the pseudo-random sequence generator is unnecessary.