A method is provided for estimating a temperature distribution history in the case of line-heating flat-plate steel by high frequency induction. The method of estimating the temperature distribution history includes a first step of measuring a history of temperature distribution that is generated when a test piece of sheet steel is spot-heated; a second step of analyzing an induction current distribution that is generated when the sheet steel is spot-heated; a third step of expressing the induction current distribution by an approximation equation of the initial induction current distribution at an initial temperature and temperature dependent correction factor of the initial induction current distribution, and identifying the initial induction current distribution and the temperature dependent correction factors based on the temperature distribution history and the induction current distribution; a fourth step of analyzing internal heat generation from the initial induction current distribution, the temperature dependent correction factor, and a temperature dependency of electrical resistivity of the sheet steel; and a fifth step of analyzing the temperature distribution history generated during the line heating by applying the internal heat generation to the sheet steel while the internal heat generation is being moved. According to the method, the temperature distribution history in the case where the flat-plate steel is line-heated by high frequency induction can be efficiently estimated at high precision.