GH984G is a new Ni-Fe-Cr base alloy which has been designed for use as superheater, reheater and header materials for boilers in 700 ℃ advanced ultra-supercritical (A-USC) coal-fired power plants. Compared with the CCA617, Nimonic 263 and IN 740 alloys, the GH984G is an economic alloy due to the elimination of Co and it containing more than 20%Fe. As a precipitation hardened alloy, the size of γ′ precipitates has great influence on the tensile properties. The γ′ precipitates become coarse during long-term thermal exposure. The coarsening behavior of γ′ precipitates is closely related with Ti/Al ratio. However, there are few investigations about the influence of Ti/Al ratio on the coarsening behavior of γ′ precipitates of GH984G alloy. Therefore, in this work, the coarsening behavior of γ′ precipitates and its influence on tensile properties of GH984G alloy with two Ti/Al ratios was investigated during long-term thermal exposure. The results show that the growth kinetic of the γ′ precipitates can be explained by Lifshitz-Slyozov-Wagner's theory of element diffusion controlled coarsening during long-term thermal exposure at 700 and 750 ℃. The rate of γ′ precipitates growth of the alloy with high Ti/Al ratio is higher. At 800 ℃, the rate of γ′ precipitates growth decreases with increasing the thermal exposure time. The coarsening behavior does not follow the Lifshitz-Slyozov-Wagner's theory. The reasons are attributed to the effect of elastic interaction energy and the depletion of γ′-forming elements in γ matrix. The Ti/Al ratio has no obvious influence on 700 ℃ tensile properties during long-term thermal exposure between 700 and 800 ℃. The 700 ℃ yield strength has no obviously decreases even if after thermal exposure at 700 ℃ for 10480 h. The ductility increases after thermal exposure at 800 ℃. The variation of strength and ductility is attributed to the coarsening of γ′ precipitation. The deformation mechanism is the moving dislocations shear γ′ precipitates and the stacking faults form in γ′ precipitates. The fracture mode is the mixture fracture mode. The Ti/Al ratio has no significance influence on the deformation mechanism and the fracture mode.