Abstract: To explore the variation of pedestrian density in the merging channel of subway station, a modified lattice gas model with biased random walkers was proposed to simulate the aggregation process of pedestrian flows in Y-shaped channel in peak time under open boundary conditions. The model consisted of square and triangular lattices, and QT simulation program was used to mimic the pedestrian flow in channels intersected at any angle. By analyzing the phase transition characteristics of pedestrian flow densities in both branch channels and merging channel, the density phase diagram was obtained. Studies show that the pedestrian flow density of the merging channel changed with variation of the width and offset angle of the branch channels, combined with theoretical analysis to prove the accuracy of the simulation results. It is found in the study that for a Y-shaped channel with the same branch channel width, the dynamic transition of Y-shaped channel occurs at density of branch channel is 0.4 and 0.3 respectively, and the merging channel density is at around 0.5, but when the widths of branch channels are not the same, the critical density of merging flow decreases with the channel width ratio increase and increases with the offset angle increase.