Abstract: The parameters of overhead transmission lines in power system are greatly affected by complex environmental factors such as temperature, humidity, light, wind, rain and lightning.The traditional calculation of available transmission capacity is often based on the static parameters of transmission lines and the fixed current carrying transmission limit, ignoring the dynamic changes of transmission line parameters and current carrying capacity under the environmental impact.According to this problem, it proposes an available transfer capacity calculation method based on MI-LSTM transmission line dynamic parameter correction.Mutual information is used to quantify the influence of environmental factors on transmission line parameters under different spatial-temporal states, corrects the input characteristics of neural network, and predicts the transmission line dynamic parameter in real time.Dynamic parameters are used to correct the dynamic power flow limit of transmission line and calculate the line power flow, and the available transmission capacity of power system is calculated.Combined with the actual weather and line parameter data in Northeast China, the example is calculated in IEEE14 bus system to verify the effectiveness of the proposed method.