Diffusion coefficient always attracts more attention because of its prediction for diffusion in a glassy polymer. However, most of the direct measurements of diffusion coefficients are time-consuming, expensive and system intrusive. Here, we report a facile method to measure apparent diffusion constant on the cross-section of thin PVA film with a device, which is structured with a thin conductive film, employed diffusion and the solution conductivity theory well. The diffusion time and the conductivity of the device are determined by the process of solution passing through the cross-section of thin PVA film and reaching the conductive substrate. The data detected the apparent diffusion constant in diffusion and the concentration gradient of the solution on the interface between the PVA film and conductive film. This device provides a simple, rapid and effective way to study the apparent diffusion constant in PVA film.