The invention discloses an oil reservoir ignition time determination method and device. The method comprises the steps that the rapid combustion temperature of an oil product, the spontaneous ignition point temperature and the ignition radius of the oil product, the initial temperature of an oil reservoir and the basic parameters of the oil reservoir are obtained; the farthest end, away from a well drum, of the ignition radius corresponds to the end point of the maximum ignition radius; an initial model that the heat quantity of air is equal to the difference value of the stored heat quantity and the heat quantity of heat loss of a top cap layer and a bottom cap layer is built through the energy conservation principle; the initial model is simplified to obtain a calculation model used for determining the parameter of a stratum temperature field, wherein the parameter of the stratum temperature field is a dimensionless variable; the ignition temperature is determined according to the rapid combustion temperature of the oil product; and the obtained ignition temperature, ignition radius, the initial temperature of the oil reservoir and the basic parameters of the oil reservoir are substituted into the calculation model to determine the ignition time of the oil reservoir. By adoption of the oil reservoir ignition time determination method and device, the ignition time needed by the oil reservoir can be accurately determined.