In order to decrease the quantity of crystal bundary, dislocation, micro-defect and transition group impurity contained in multi-crystalline silicon and further to increase solar cell′s photoelectric conversion efficiency, the silicon wafers were preprocessed for solar cell utilizing the laser pulse which was produced by TEA CO2 laser. The laser pulse duration is about 200 ns and the wavelength is about 10 ?滋m. Multi-crystalline silicon wafers were placed in 20 mm Hg hydrogen gas and irradiated by different wavelength laser pulse and different pulse numbers, twenty-five samples were manufactured. After removing the affected layer, the sample′s electrical resistivity was metered using S2T-2A four point probe tester. The result shows that all sample′s electrical resistivity is cut down in different degree. Specifically the sample′s electrical resistivity decline rate is the largest and its maximum is 50%, which is irradiated by P18 and P20 brunch and irradiated by three pulses. The lifetime of minority carrier of all samples was tested with high frequency photoconductive lifetime tester, the outcome of experiment indicates that all sample′s minority carrier lifetime is increased. Especially the samples lifetime is raised largely which are irradiated by P18 and P20 brunch and irradiated by three pulses, their increasing amplitude reaches 30%.