Abstract: Recent studies on two phase flows in gas-solid fluidized beds were retrospected, and the development in nonlinear mechanism studies was outlined. The chaos studies indicate that fluidized bed systems are determinacy chaos systems and the results of the dissipative structure theory attribute fluidized bed systems to non-equilibrium thermodynamic ones. The analyses of stochastic force on fluidized bed systems apply the stochastic theory to flowing mechanism and studies of bubble distribution, and redound to open out the inside nonlinear mechanism and characteristic of fluidized beds.