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Using hydrogen as an alternative fuel in spark-ignition engines has great potential for reducing exhaust emissions. Hydrogen engines have CO2- and HC-free combustion and lean operation, offering lower nitrogen oxide (NOx) emission. In this paper, a numerical study of a direct injection spark-ignition (DISI) hydrogen-fueled engine was conducted via 3-dimensional computational fluid dynamics (CFD) methods and results were compared with experimental data, showing good agreement. Injection timing, initial charge temperature, and initial charge pressure were selected as effective and controllable parameters of emissions and performance characteristics. Results showed that mixture homogeneity was more affected by injection timing, and advancing the injection timing led to improved engine performance with a slight increase in NOx emissions. Increasing the initial pressure and decreasing the initial temperature led to better engine performance and reduced NOx emissions in the DISI hydrogen-fueled engine.