The effect of spark timing on combustion and emissions of a hydrogen direct injection stratified gasoline engine was investigated. The engine was operated at 1500 rpm and excess air ratio at 1.2. It was found that when the hydrogen volume fraction was raised from 0% to 10%, and the hydrogen injection timing was 110 degrees CA BTDC a good stratified effect was achieved. The spark timing was varied from 4 to 16 degrees CA BTDC. This test demonstrated that the brake thermal efficiency first rose and then fell with the spark advance angle increased. In addition, it increased with the increase of hydrogen volume fraction. Postponing the spark timing caused the maximum instantaneous heat release rate increase. The peak cylinder pressure and the maximum rate of pressure rise increased with spark advance angle increase. Postponing the spark timing also caused NOx, HC and CO emissions to decrease. When the hydrogen volume fraction increased, the NOx emissions rose and the HC and CO emissions dropped. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.