To solve problem of data jitter caused by direct usage and switch of various altitude sensors on unmanned aerial vehicle（ UAV）

a seamless altitude fusion method is proposed based on micro inertial device /GPS / sonar / barometric altimeter. Error models for sonar and barometric altimeter are established

and dynamic errors are analyzed and preprocessed. With seamless fusion method

altitude variation is obtained to calibrate barometric height. To get more accurate altitude

data of barometric altimeter

GPS and inertial navigation system are effectively fused by unscented Kalman filtering（ UKF） method. This method takes error characteristics of various height sensors into consideration

can solve jitter problem when modes switching. Flight experimental result shows that designed system has high precision and reliability after fly for 150 s

error of altitude estimation obtained by this method reaches to 0. 470 7 m. It can meet flight requirement of UAV.