Abstract: The vector observation algorithms is applied to GPS attitude determination.The traditional TRIAD algorithm only uses two non-collinear vectors to determine three-axis attitudes.But it is sensitive to the master vector and can't use the third vector.An improved TRIAD algorithm is presented which efficiently resolve the problem of sensitive to the vector selection.In order to employ all measurements from three basslines,a new algorithm named fusion TRIAD is proposed on the basis of the OPTTRIAD algorithm.The fusion TRIAD algorithm can improve the accuracy of attitude solution obviously.The experiments are made by TANS vector GPS receiver.The results show that the sensitivity to the master vector actually disappears in the improved TRIAD algorithm.Compared with the traditional TRIAD algorithm,the fusion TRIAD algorithm can improve the accuracy of attitude solution 35%,19% and 34% in azimuth,pitch and roll respectively.