Abstract: According to the deficiency of the LLL algorithm(A.K.Lenstra,H.W.Lenstra,L.Lovasz algorithm),the adaptive integer orthogonal transformation algorithm is proposed in the paper.It can be used to improve the LLL algorithm with sort ascending matrix.Based on the condition number,comparison has been made between the LLL algorithm and the improved LLL method by using 600 symmetric and positive definite matrixes derived from random simulation,and as 30 sets of actual measuring data.Numerical results show that the improved LLL algorithm has better performance in decreasing matrix condition number and the number of candidate integer ambiguity.Thus it could decrease the searching time of the right integer ambiguity resolution.