The fixed electricity price mechanism has been adopted in the medium-long trans-provincial electricity market in China，but it is unable to play the regulation role of the electricity market. To solve the shortcomings of the fixed price mechanism，the principle of electricity-dividing according to the trading agreement curve and the execution curve are proposed，and the mechanism of time-sharing price settlement is analyzed. According to the occurrence period of the external power of the curve and the power scale ，three different pricing mechanisms for the external power of the peak and valley curves are proposed. Finally，the calculation cases of the extra-curve price and transaction cost of the mechanism are carried out，which quantitatively explain the influence of the deviation power scale on the settlement price under different pricing modes，and achieve the purpose of guiding the market entity to consciously perform the contract according to the curve of the transaction agreement.