A plant operation assistance system (100) includes: a data obtaining unit (101) configured to obtain monitoring data indicating state quantity of a plant, the state quantity being detected by a sensor (10); an identifying unit (102) configured to identify, based on the state quantity, a probability distribution of the monitoring data; a model generation unit (103) configured to generate, based on a plant parameter composed from a database including design information of the plant, a stochastic model of the plant; a data processing unit (104) configured to assign the probability distribution to the monitoring data obtained by the data obtaining unit; and a prediction unit (105) configured to input the monitoring data assigned with the probability distribution, into the stochastic model, and predicts a state of the plant.
