This study aims to optimize the inbound traffic flow on on-ramps by considering low time costs, good speed stability, and high driving safety for mixed traffic flow. The optimal inlet gap is identified in advance, and trajectory guidance for vehicles entering the gap is determined under safety constraints. Based on the initial state and sequence of vehicles entering the merging area, individual vehicle trajectories are optimized sequentially. An optimization model and method for ramp entry trajectories in mixed traffic flow are developed, incorporating on-ramp vehicle entry sequencing and ordinary vehicle trajectory prediction. Key performance indicators, including driving safety, total travel time, parking wait probability, and trajectory smoothness, are compared and analyzed to evaluate the proposed approach.