Abstract: Radiation effect of the device becomes more important with the development of aerospace due to them may change the state or even destroy the device. The major types of the radiation effect include single event effect (SEE), total ionizing dose (TID) and displacement damage (DD). SEE can be caused by ions incidence the sensitive region of the device and changes the potential of the electrode. TID can be caused by ions incidence at the material of the device and leads to the charge accumulate on the Si-SiO₂ interface. In general, the SEE and TID often occur in random-access memory (RAM), and the DD often occur in image sensor. Therefore, the researching and estimating the risk of radiation effect on the device before use is necessary. Much study has been report during the last decades, but most of them focus on the single radiation effect. Recently, the synergistic effect becomes attention because the development of space nuclear power and it reflectes the real radiation environment of the device. In this paper, the static random access memory (SRAM) was used for research the synergistic effects by using the China Institute of Atomic Energy HI-13 Tandem Accelerator and the ⁶⁰Co irradiation device. The SRAM was radiated by the gamma ray and then the different heavy ions. Yet it’s worth noting that the sequential irradiation method is a common research method of synergistic effect. In the total ionizing dose experiment, different doses on the device were chosen, such as 300, 500 and 750 krad(Si). Meanwhile, the dose rate keeps the same on 90 krad(Si)/h. In the single event effect experiment, different ion energy on the device was chosen, such as 5.0, 13.9, 21.9 and 37.4 MeV·cm²/mg. The time interval between two different radiations keeps brief for decreasing the annealing effect. Single event upset of the device was measured by the self-developed testing system. A typical soft errors calculation method under the mixed beam environments was proposed. By using this method, the on-orbit soft errors of the device in the space nuclear power were calculated. Meanwhile, the uncertainty of the method was distinguished and calculated including the uncertainty of total dose, single event upset number, flux and the fitting process. Type A and B uncertainties were synthesised for the final uncertainty. Research result suggests the synergistic effects may reduce the soft errors compared to simple single event effect.