Abstract: Disclosed is a method of estimating the outflow amount for each component of the effluent of a coal liquefying reactor consisting of vessel type reactors (16a, 16b, 16c) operated under a high temperature and a high pressure. The outflow amount for each component of the effluent is assumed, and the gas-liquid equilibrium composition of the mixture of the composition within the reaction vessel is calculated. Further, the volume flow rates of the gaseous phase and the liquid phase within the reaction vessel are calculated, and the residence time (&tgr;1G, &tgr;2G, &tgr;3G), (&tgr;1S, &tgr;2S, &tgr;3S) of each of the gaseous phase and the liquid phase is calculated on the basis of the gas hold-up within the reaction vessel calculated on the basis of the volume flow rate and the empirical formula. The outflow amount for each component of the effluent is calculated on the basis of the residence time (&tgr;1, &tgr;, . . .