Abstract：Research purposes： With the continuous development of the city and the gradual construction of the subway network, the conflicts between the capacity demand and transport supply of the line R3 has become more remarkable. As the starting station of the line R3，Dalian Station′s turn-back ability limits its transport capacity, so the transformation of Dalian Station is necessary and urgent. In this paper, the station′s turn-back ability after capacity expansion and the switch adaptability after the lateral speed hoisting have been studied. A new expansion plan about the station-front turning-back has been put forward by comparing the construction projects of the station-front and station-post turning-back. This result has great significance to the full range of capacity expansion project.  Research conclusions： (1) The calculation result of station-front turn-back capacity shows that line transportation capacity can be improved by increasing speed of train that running through the turnout in the side direction and expanding the train formation. (2) For the design of the station-post turn-back project，it needs to first calculate the turn-back capacity after the station expansion, and then according to the construction conditions to make reasonable capacity expansion plan. (3) The choice of capacity expansion plans should minimize the impact on the line operation and at the same time，pay attention to both the economic benefit and the project coordination difficulty, thus choosing the optimal solution. (4) The research results can provide a reference for the selection of other similar line expansion and expansion.