A series of thermosetting polyimide oligomers with different calculated number-average molecular weights (M_n) were synthesized. Thermosetting polyimide (TPI) specimens were produced by a hot-pressing technique. This paper investigates the effect of the calculated number-average molecular weight (M_n) on tribological properties under high temperature. Worn surfaces and transfer films morphologies were observed using SEM to reveal the wear mechanism. Experimental results demonstrated the relationship between M_n and tribological properties. The research discussed transition temperature of wear mechanism of TPI specimens. It revealed that the transition of wear mechanism from slightly adhesive to hardly adhesive wear occurred at lower temperature, with increasing M_n. And TPI-3 prepared from polyimide oligomers (M_n=3000), presented superior performance than TPI-5, TPI-7 and homologous thermoplastic polyimide.