An important parameter in the TLP welding process is the time required for complete isothermal solidification. In this study, KCo10 intermediate layer was mainly used for the tests, which were carried out at temperatures of 1030 ℃, 1050 ℃ and 1080 ℃ (1303 K, 1323 K and 1353 K) with different holding times. The average ASZ size was measured using the solid solution on both sides of the eutectic liquid phase as the boundary. By measuring the size of the ASZ with the square root of the variation of the welding time, data fitting was used to derive a linear relationship between the ASZ size and the bonding time, and then a mathematical model of the isothermal solidification process was established based on Fick"s second law of diffusion equation with time, and the isothermal solidification time tIS was simulated and solved so as to predict the approximate time required for isothermal solidification, and was experimentally verified The accuracy of the mathematical model in predicting the isothermal solidification time was verified experimentally.