K4002 alloy is a widely used nickel-based superalloy, and the trace element Se content is not controlled by itstechnical standards. Moreover, existing studies have shown that the effects of Se on different alloys are not the same. Todetermine the influences of Se on the structures and properties of the K4002 superalloy, the equilibrium precipitated phasesof the K4002 superalloy were calculated by thermodynamic software, and the effects of Se on the microstructure andproperties of the K4002 alloy were studied. The results show that the main equilibrium precipitates of the K4002 alloy arethe matrix γ phase, γ′ phase, M3B2 type borides, carbides (MC type, M6C type and M23C6 type) and a small amount ofthe Ni5Hf phase. MC-type carbides are enriched in Hf and Ta, M23C6-type carbides are enriched in Cr, M6C-type carbidesare mainly enriched in W and contain a certain amount of Ni and Cr, and M3B2-type carbides are mainly enriched in W andcontain a certain amount of Cr. With increasing Se content, the average durability life of the K4002 alloy decreasesgradually. This is due to the continuous increase in Se segregation at the grain boundaries and the gradual formation oflow-melting point phases and even microscopic pores, which weakens the strength of the grain boundaries. The Se contentin the K4002 alloy should be controlled below 3×10-6.