Objective：To evaluate intrapelvic pressures during laser lithotripsy using different semi-rigid and flexible ureteroscopes. Methods：Intrapelvic pressures was measured on a porcine cadaveric urinary system model with two size of semi-rigid ureteroscopes （Wolf F6/7.5 and Wolf F8/9.8） and two models of flexible ureteroscopes（Polyscope and Olympus URF-P6）. 200 μm Holmium laser fiber was placed into the working cannel previously. The semi-rigid ureteroscopes were placed in distal ureter，middle ureter and ureteropelvic junction and the flexible ureteroscopes were fixed in ureteropelvic junction. Intropelvic pressure was recorded at irriga－tion pressures of 50，100，200，300，400，500 cmH2O. Results：There is a linear correlation between intrapelvic pressures and irrigation pressures. The intrapelvic pressures raised slowly when the semi-rigid ureteroscopes were put at distal ureter. The intrapelvic pres－sures raised at the fastest pace when the semi-rigid ureteroscopes were placed at ureteropelvic junction. The intrapelvic pressures using Wolf F6/7.5 ureteroscope were lower than that using Wolf F8/9.8 ureteroscope at the same irrigation pressure. The intrapelvic pres－sures of semi-rigid were higher than those of the flexible ones when ureteroscopes were placed at ureteropelvic junction. According to the equation of linear regression，the value of irrigation pressures was estimated when the intrapelvic pressure reaching 40 cmH2O，and it is found that a low irrigation pressure（34.950 to 44.284 cmH2O） could rise the intrapelvic pressures to 40 cmH2O when the se－mi-rigid ureteroscopes being put at the middle and upper ureter. The safe irrigation pressure was higher（205.345 to 313.659 cmH2O） when the semi-rigid ureteroscopes being placed at the distal ureter. The flexible ureteroscopes could withstand the maximum irrigation pressure keeping the intrapelvic pressures within the safe range，and the safe irrigation pressure of Olympus URF-P6（400.457 cmH2O） was higher than Polyscope（238.419 cmH2O）. Conclusion：In order to maintain the intrapelvic pressures at a low level，thin－ner semi-rigid ureteroscope should be used in the treatment of middle and distal ureteral calculi，and flexible rather than semi-rigid ureteroscope should be used to handle proximal ureteral calculi.