Abstract: The discrete ordinates (SN) method discretizes directly spatial and angular variables, which results in angular and spatial discretization errors. How to effectively control discretization errors is essential to assure calculation accuracy. An n’th collision source method based on the ray tracing method was developed by calculating the flux density of particle collisions in a selected region. The isolated source was equivalent to the fixed source distributed throughout the computational model for discrete ordinates transport calculation. Self-designed shielding problem and Kobayashi benchmark problem were used to verify and analyze the adaptability of n’th collision source method. The results show that the n’th collision source method can effectively alleviate the secondary ray effect problem compared with the first collision source method in the self-designed shielding problem. As for the Kobayashi benchmark problem, the root mean square (RMS) of the relative error between the calculation result and the reference value is less than 3%. The n’th collision source method effectively reduces the discretization errors and provides better accuracy and reliability for the shielding calculation.