The high transient requirement of rapid start for a hybrid electric vehicle engine will inevitably make it difficult to control emission during the starting process. In order to study the engine combustion and emission characteristics under different starting transient conditions, different start methods were conducted including 24 V motor start and drag start at 800 r/min, 1 000 r/min and 1 200 r/min respectively based on a selfbuilt single-shaft parallel hybrid test platform. The research results show that the incylinder pressure peak, the mean effective pressure and the combustion duration all decrease and the reduction becomes small with the increase of the drag speed during the starting process. Besides, CO, NO_x and soot emissions also reduce. However, the combustion fluctuation is relatively high at the drag speed of 800 r/min. The combustion and emission characteristics between 24 V motor start and 800 r/min drag start have the same trend with cycle or time and the changes of them between 1 000 r/min and 1 200 r/min drag starts are the same. Generally, 800-1 000 r/min drag start is a better rapid start strategy, but the fuel injection mass at start time needs to be recalibrated.