Abstract: A stochastic approach,namely,Monte Carlo method with“tree structure pattern”has been adopted tosimulate the random backrnixing,residence time,reaction and dynamics of solid particles with size distribu-tion and with complex reaction in a complex flow system.Turbulence of particles in reactor system is simu-lated by stochastic tree pattern which is shown by pseudo-random number series picked from a uniformlydistributed set of numbers between zero and one.A Monte Carlo procedure is employed to model the par-ticles’ stochastic residence time,random flow and reaction with fluid.A large number of discrete bundlesof particles have been simulated and followed.Statistic results of all particles in the last information representthe solution to the problem under steady state of flow.The approach has a simple physical concept and simulation procedure.All calculation has been carriedout easily with a computer.For simple reaction system,results are in good agreement with those obtainedfrom the known approach and experiments.The method could provide a new kind of technique for simu-lating the behavior of particles in a continuous flow reactor.