The invention provides an engine instantaneous oil consumption determining method based on the cylinder pressure. The method includes an engine cylinder pressure sensing signals, calculating the associated combustion state indexes, adopting the combustion state indexes as independent variables with the engine speed n, adopting the engine oil consumption as dependent variables, and establishing a module. The combustion state indexes include the indicated pressure IMEP, a heat release midpoint CA50 and the accumulated released heat AHR. The method is on the basis of the principle of engine combustion, an engine instantaneous oil consumption estimating method is provided according to test data, and the precision estimation of the engine instantaneous oil consumption can be implemented by arranging a cylinder pressure sensor additionally only on the conditions that an engine combustion system and an exhaust system are not changed. Compared with the prior art, the engine exhaust detection is omitted, that the fuel is injected into the cylinder additionally in the engine fuel supply stopping state is omitted, the real-time engine oil consumption estimation under all operating condition can be implemented, and the estimation result is prevented from being influenced due to ageing of an oil injector.