For the real-time detection problem of combustion timing of partially-premixed combustion in a compression combustion engine, the algorithm in which combustion timing was detected based on the prediction of motoring cylinder pressure curve was proposed. The equivalent isentropic index that was predicted according to the self-adaptive coefficient and then predicted the curve of motoring cylinder pressure, the threshold of cylinder pressure was then set, and the combustion was identified when the difference between measuring and predicting cylinder pressure was beyond the threshold. Experimental results show that the absolute prediction error of motoring cylinder pressure is less than 20 kPa and the algorithm can real-time detect the combustion timing under the engine test conditions.