M718 alloy with an extra high Mo content of 7.50 wt％ which reduced Nb addition and increased Al and Ti additions within the composition specifications of 718 alloy has been designed to increase the service temperature of 718 alloy.And the effect of the heat treatment on the microstructure and mechanical properties of M718 alloy has been investigated in this study.The results showed that Laves phase precipitated on the grain boundaries of M718 alloy instead of δ-Ni3Nb phase in 718 alloy,and γ“ and γ\'phases precipitated in the matrix of M718 alloy as that in 718 alloy.Increasing the solution temperature from 960 to 1050 ℃ noticeably reduced the intergranular precipitation of Laves phase.The precipitation of Laves phase was appropriate at 1020 ℃ for improving the grain boundary cohesion.Increasing the two-stage aging temperatures markedly increased the sizes of γ” and γ\'phases.As a result,the strength of M718 alloy increased.