This study employed the VG model to characterize soil water diffusivity, predefined model parameters, and utilized the Philip method to calculate Boltzmann parameters corresponding to varying water content (θ - λ data). Compared to the test values, the interior point method was used to determining model parameter. Consequently, an iterative method for determining soil water diffusivity was proposed. The applicability of the proposed method was verified through the Hydras-1D simulation and existing literature data. Results revealed that with a testing error of less than 10% in water content, the determination coefficients of the calculated soil moisture diffusivity consistently exceeded 0.995 0. When analyzing data on temporal water content variations (θ - t data), the critical water content which was influenced by boundary effects exerted minimal impact on the calculated outcomes, and even if it was below 0.280 m³/m³, the determination coefficient of the calculated results remained above 0.997 0. By contrast with existing methods, this method can offset difficulties of accurately determining soil water diffusivity in high water content ranges when the test data is θ - t data. Therefore, it is evident that the proposed method can accurately determine soil water diffusivity, with minimal influence from testing errors and critical water content. These above findings can provide reliable values for soil water diffusivity, aiding in the simulation of soil water movement.