With the increasing penetration of renewable energy, a pricing method with higher granularity is needed to reflect time-varying market supply and demand. Based on multi-parametric programming theory, this paper proposes a time-continuous locational marginal price (time-continuous LMP) calculating method. The proposed method builds the economic dispatching model with time as the planning parameter, and deduces the analytical expression between LMP and time based on multi-parametric programming theory. In this way the continuous mapping relationship between LMP and time can be obtained directly. This can provide the market with time-continuous price signals. Simulation results based on IEEE30-bus and IEEE118-bus systems demonstrate the reasonableness and effectiveness of the proposed method. This work is supported by the National Natural Science Foundation of China (No. U2066209) and the Fundamental Research Funds for the Central Universities (No. 2020CDJQY-A025).