We discussed the proposal and process of arraying source racks in the second time source adding for BFT-IV irradiation device in Zhongjin Irradiation Incorporated Company (Chengdu Branch), and calculated the optimized proportion of each module’s activity among total 16 modules’ by theoretical calculation. The new radiation source was added to each module with the optimized proportion. The new radiation source racks were arrayed in each module in a uniform manner. The dose mapping was calculated by MCNP-4C with the mathematical model which was validated by the result of the first time dose mapping test. The optimal scheme of arraying source racks was selected through calculating multiple scheme of arraying source racks by MCNP-4C. The source racks were loaded with the optimal scheme of arraying source racks. The energy utilization efficiency is 16.7%, and the max uniformity is 1.36 in the dose mapping test for 0.1g?cm–3 products after the second time source loading. The result is better than that of first time source loading. It proves that the method and the scheme of source arraying are reasonable and effective.Cited