Lattice Boltzmann method is adopted to numerically analyze nonlinear characteristics of double diffusive mixed convection in an enclosure. A heated cylinder is located at center of the enclosure. Fluid flows from an inlet at lower-left wall of enclosure and an outlet is at upper-right,upper-middle and upper-left wall respectively. Simulation results indicate that there are steady stationary solution,periodic and aperiodic oscillatory solutions in double diffusive mixed convection at different parameters. Phase path of velocity of monitoring point finally reaches a point,a closed loop and irregular curves,respectively.