The power flow model is usually used to estimate power from the central calculation for the whole power system. In recent years, data-driven approach is an emerging technique to determine power flow without knowing circuit parameters. However, with the development of renewable energy, more complex power grids are placing an increasing burden on central computing. Therefore, this paper proposes a method to estimate power from a single bus only which provides a quick reference to the power of a single bus. This method is based on modified linear power flow model, the core is to solve the challenge of power estimation using only one single bus data rather than whole power system data by analyzing the electrical relationship. The proposed modified linear power flow model includes both the nonlinear physical power flow model and the linear regression model. Simulation results on the IEEE Standard bus 30 show that this method has higher accuracy than other linear power flow models in single bus power calculation.