Abstract: Shielding calculation is an important basis for the design and optimization of nuclear facilities. The MC-S_N coupling algorithm can effectively solve the problem of complex geometry and deep penetration problem. This algorithm converts the particle track information produced by the Monte Carlo program into the boundary angle flux density of the discrete ordinate method. It is necessary to calculate the particle information of the corresponding angle region in each discrete direction. The method of dividing the angle region by the latitude and longitude lines affects the particle balance during the conversion process. Usually the angle flux density can be expanded by the spherical harmonic function. Based on the layer symmetric quadrature set and Legendre-Chebyshev quadrature set, the accuracy of the coupling method for the spherical function of each order was analyzed. The results show that the discrete angle region division of the coupling method has high accuracy for the conversion of the low-order spherical harmonic function. But it has a great influence on the precision of the high-order spherical harmonic function. The average deviation of the second-order spherical harmonic conversion accuracy is above 10%. Due to the greater correlation of the angle regions of the high-order quadrature set, the conversion precision is significantly higher than that of the low-order quadrature set.