The incylinder direct injection hydrogen system design was designed on a 1.5 L exhaust gas turbocharged intake intercooled 4-cylinder gasoline engine. NO_x, HC and CO emission performances of direct injection hydrogen engine were studied under different excess air coefficient(λ) combustion modes. The results show that the economy of hydrogen engine improves more than 30% compared with gasoline engine. The excess air coefficient and load have a significant impact on NO_x emissions under the load of 0.2 MPa and 0.28 MPa at 2 000 r/min. NO_x emission reaches the peak when the lean burn of hydrogen works at the excess air coefficient of 1.1 and the peak will be higher at the higher load. The combustion phase maintains at the optimal level of 8° after top dead center at low load, and can be controlled to be near the optimum by the lean combustion mode and the adjustment of ignition advance angle at high load. In all working conditions of the test, the ultra-lean combustion mode with the excess air coefficient close to 3 can be achieved by installing an electric charger. When λ is larger than 2.7, NO_x emission is close to zero. At the same time, HC and CO generated by oil consumption can be effectively reduced to a level of near zero  emission of less than 5×10^－6 through optimization of the tension of piston ring group. 