The effects of grain boundary carbide on crack propagation behavior of GH864 alloy were studied at 650 oC after different heat-treatment. The results indicate that the pattern of grain boundary carbide of GH864 alloy is gradually evolved after different heat-treatment, i.e. little particle→discontinued→continued→necklace→closed. The precipitation of grain boundary carbide strengthens the grain boundary and decreases the crack growth rate. The change tendency was concluded between the grain boundary carbide continuous factor and the crack growth rate. When the grain boundary carbide continuous factor is below 1, the crack propagation resistance increases with increasing the size of grain boundary carbide and grain size. The comprehensive interaction effect between the grain size and grain boundary carbide was also concluded. The optimum crack propagation resistance may exist when there is the lowest point in the interaction effect between the grain size and grain boundary carbide