The voltage grade of main Xian power grid is 330/110 kV. In the initial development stage of power grid, the 300 MW grade generation units are all required to interconnect to 330 kV power grid. However, with the development of the urban load and power grid, the connection principle is not adaptive to the development of power grid completely. Therefore, taking the connection to power system of 2×350 MW generation units in Xian west suburb thermal power plant as an example, the feasibility, rationality and essential technology conditions are analyzed for the 300 MW grade generation unit connecting to 110 kV power grid by the sub-layer and sub-area way.