This paper analyses the problems existing in the probability mod el of hydrocarbon amount, and proposes the hydrocarbon amount probability model of volumeunit hydrocarbon\|generating method. It proves that the hydrocarbon amount predicted by this method is close to the expectation of the model, and that the esti mation interval becomes obviously small. The basic procedure of this method is to divide the local petroliferous geological unit into many volume units, and get an estimator of every volume unit whose volume is not zero with the Monte Carlo method. The sum is an estimator of the hydrocarbon amount of local petroliferous geological unit.The distribution curve of the local petroliferous geological unit of the hydroc arbon amount can be drawn by a series of estimators got from repeated computations. So the hydrocarbon amount of the evaluation area can be calculated by the simulated computation of every local petroliferous geological unit