Taking the WC nozzle with obvious difference in laser shock resistance performance used in laser jet solder ball bonding as the research object, the difference between microstructure and composition was observed by means of scanning electron microscope/energy dispersive X-ray spectrometer. Combined with the theory of material beam interaction, the micro mechanism of the influence of Co content and microcracks on the laser resistance of WC nozzle was studied. The test results show that WC particle size, through microcrack, and metal binder Co content are obviously different. The analysis shows that the through microcracks caused by excessive sintering pressure will produce light trapping phenomenon to the laser, and form a heat affected zone with higher temperature around it, in which the Co with lower melting point is easy to melt. Near the heat affected zone at the front end of the nozzle small hole, the molten Co and tin ball are prone to metallurgical reaction, forming tin, and the nozzle will fail in severe cases. The more serious the crack and the higher the Co content, the worse the resistance to laser shock of WC nozzle. Therefore, reducing Co content and sintering pressure can effectively improve the laser shock resistance of the nozzle.