When there is maneuvering acceleration,low-accuracy Attitude and Heading Reference System (AHRS) cannot measure the gravity accurately,which will cause large errors in horizontal attitude,if we still use the output of the accelerator to calculate the attitude.In order to weaken the influence of maneuvering acceleration and improve the estimation accuracy of horizontal attitude when there is maneuvering acceleration,an adaptive Kalman-filter horizontal-attitude estimation algorithm is proposed.A pseudo-measurement equation is established by taking the attitude quaternion and gyro drift as state variables,taking the quaternion attitude-update differential equation as the state equation,and taking the output of accelerator as measurement variables.Based on the residual error of accelerator output update,the variance matrix of measurement noise is estimated in real time and dynamically adjusted.This method solves the problem of horizontal attitude estimation of AHRS under the influence of maneuvering acceleration,and improves the estimation accuracy of horizontal attitude.Driving tests have verified the effectiveness of the proposed algorithm.