The cryo-electron microscopy (cryo-EM) single-particle reconstruction problem is always challenging.Three-dimensional structure determination by analysis of cryo-EM images requires many parameters to be determined from extremely noisy data.RELION developed by Scheres et al uses a Bayesian approach to infer parameters of a statistical model from the data [1].Our researches yield new solution into orientation problem of single-particle analysis.Two Euler angles instead of three Euler angles will be determined under correlation function.Then third Euler angle is confirmed by maximum likelihood method.Our implements will have computational complexity decreases from O(n3) into O(n2+n).Implementation of initial research show it work well in reducing the computational costs.In the future work, we plan to improve this algorithm and develop more efficient methods to improve image reconstruction process.