Simulation of pedestrian evacuation from a room with multi-exit and asymmetrical pedestrian layout is presented based on an improved dynamic parameter model in this paper. The computation and the count-area of imaginary distance are improved based on the Max-Min evacuation path selection of actual and imaginary distance in order to reduce evacuation imbalance caused by the asymmetry of pedestrian layout. An imbalance coefficient is introduced to describe the asymmetry of pedestrian layout. The effects of pedestrian layout asymmetry on the evacuation time are analyzed respectively from fixed and unfixed pedestrian initialization site. The simulation results of the improved and original models are compared and analyzed, and the improved model can effectively reduce evacuation imbalance. Simulation results show that under normal evacuation condition with considerring reasonable pedestrian and jam around exits, evacuation time is hardly affected by pedestrian and exit layout and depends mainly on cognition coefficient, total width of exits and pedestrian initialization amount.