Abstract: The relations among Rodrigues parameters,modified Rodrigues parameters and quaternion were described.A method based on modified Redrigues parameters was proposed,which can avoid odd value.The differential equation and attitude matrix based on Rodrigues parameters and modified Rodrigues parameters were educed.By simulation,the computational complexity and calculation accuracy are compared among secondary planet attitude algorithms based on Rodrigues parameters,modified Rodrigues parameters and based on quaternion.The simulation results show that the calculation accuracy of the method based on the Rodrigues parameters and modified Rodrigues parameters is equal to that based on the quatemion,and the computational complexity of the former one is less than that of the later.