On the basis of considering reactive power injections and line resistance, a novel DC power flow algorithm, which takes into account the influence of grounding branches without losing the linearity of DC power flow equations and is suitable to calculate reactive power flow in transmission system, is proposed. The shunt elements in grounding branches are included by utilizing the complete nodal admittance to form corresponding admittance item，and the linearity of DC power flow equations is retained. Nodal voltage amplitude of PQ node could be obtained by the back substitution of modified voltage phase angles. The active power flow and reactive power flow could be solved using the complex power flow equations. IEEE 118-bus test results indicate that compared with DC power flow method without the consideration of grounding branches, the proposed method retains the performance of current DC power flow algorithm in the calculation of active power flow while improving the accuracy of reactive power flow and nodal voltage amplitude, which makes DC power flow method be suitable for calculating reactive power flow in transmission system. This work is supported by National Natural Science Foundation of China (No. 51467012 and No. 51167012) and Scientific Item of Education Bureau of Jiangxi Province (No. GJJ14165).