Abstract: According to the characteristics of a cobalt-60 irradiation facility, we have built a more realistic model by using Monte Carlo software MCNP5, taking the center of the two source racks as the coordinate origin.In order to check the source distribution scheme, the absorbed dose distribution of the reference plane was simulated. The average absorbed dose in one carrier under different chain speeds and different numbers of the total carriers (48 carriers, 24 carriers, 16 carriers, 8 carriers) were calculated. Compared to the measured value, the calculation results showed that the average relative deviation between the simulated and measurements was less than 10%, which means the model and the simulation result established by MCNP5 are accurate and credible. It can describe the dose distribution in products in the carriers, which will provide guidance for the real work and research.