In order to improve the filtering performance of the high-degree cubature Kalman filter(CKF), a high-degree cubature Kalman filter based on the diagonalization of the matrix is proposed. Based on the high-degree cubature rule, the diagonalization of the matrix is used to take place of the Cholesky decomposition and the square-rooting matrix of the covariance can preserve the information of the original feature space, so that the state statistics can be calcuated accurately and the filtering accuracy is improved. At the same time, the diagonalization of the matrix does not require the condition that the covariance matrix must be the positive definite matrix and the stability of filtering algorithm is enhanced. The simulation results show that the proposed algorithm is feasible and effective, and it can obviously improve the fltering effect of the standard high-degree CKF algorithm.