The research of overpressure prediction and detection has long been concentrated on under-compaction, the overpressure originated from hydrocarbon generation was thought difficult and even impossible to be predicted and detected. In order to predict and detect the pressure originated from hydrocarbon generation, we compared the characteristics of under-compaction strata with that of source rocks, and studied the changing of pressure caused by hydrocarbon generation with depth. The results show that the socalled under-compaction actually is the combined response of genuine under-compaction and hydrocarbon generation, the pressure generated by hydrocarbon generation could also be predicted and detected while drilling. Based on that, the method distinguishing their contribution and the predicting and detecting methods, such as exponent and neural network, are put forward. This research result renew the viewpoint that the overpressure originated from hydrocarbon generation couldnt be predicted and detected, so, it contributes to improve geology understanding about overpressure and the level of overpressure prediction and detection.