Abstract: VSOP code is widely used in the engineering design of the pebble bed high-temperature gas-cooled reactor (HTR), and the verification and validation (V&V) are required to this code. Based on the same reference of HTR reactor core, the results from VSOP code and Monte-Carlo code were compared, and the random distribution of pebble bed was treated as the repeated structure of special shape in Monte-Carlo model. The homogenized channels in side reflector and equivalent cones in pebble bed were adopted in VSOP model, and the deviation of k_eff aroused from these simplification treatments was analyzed by Monte-Carlo model. The results show that the final difference in the k_eff between VSOP model and detailed Monte-Carlo model is not significant, which implies that the VSOP model is applicable and reasonable. Of course, the V&V on VSOP code and model should be further extended.