Femtosecond laser processing has litle-thermal effects, high precision, and is not particular about materials. Aiming at the machining requirement for nozzle′s spray holes, as a key part of the high pressure common rail injection system for diesel engine, a femtosecond laser processing apparatus with three-wedge scanning system was designed for technical research of taper holes′ machining. Then tests of the taper holes′ physical dimensions and the flow rate of the fuel jet nozzles were carried out with three coordinates measuring machine (measurement accuracy 1.2 μm) and high-pressure liquid flow test bench for the injector(measurement accuracy ±0.1%). The experimental results show that the designed apparatus can machine nozzles, and the performance is able to meet the application requirement of Euro V emission regulations. The technique has important significance for improving the level of automobile industry and domestic emission standard of diesel engined car.