To realize the autonomous flight and the automatic correction of the attitude of the micro air vehicle this paper designs an automatic detection method of attitude angle based on frontview camera. Through the parameter optimization calculation of the image linear discriminant function, the linear equation parameters of the horizon in the image are extracted and the roll angle and pitch angle of the aircraft are calculated. At the same time, this paper improves and optimizes the optimization calculation process, which greatly reduces the computational complexity Finally, the experimental results are verified by the actual flight images Due to reliable roll angle detection low computational complexity and easy hardware implementation, the experiments show that the proposed method is suitable for low cost micro air vehicle platform without attitude measuring device.