By measuring magnetization curves of polycrystalline Tl2Ba2Ca2Cu3Oy superconductor, magnetitudes of the hysteresis against temperature T and applied field Ba have been obtained. Using the critical state equation, we have got an effective pinning force which varies with temperature and field and results from both contributions of winklinks and intragrain pinning. Peak effect of the effective pinning force has been found, and the peak moves to higher fields with temperature dropping. The peak effect is considered to be the results of two pinning mechanisms, which have different field relations. Finally, some discussions about the results are made.