An inverse model is used to estimate the wall heat flux in film condensation on a horizontal disk. The inverse analysis is based on film condensation thickness readings taken at several different points on the plate. Finite-difference methods are employed to discretize the problem domain, and then a linear inverse model is constructed to identify the unknown conditions. This approach rearranges the matrix forms of the governing differential equations and estimates the unknown surface conditions. Then, the linear least-squares method is adopted to find the solution. Unlike other methods, the proposed inverse analysis method requires no prior information regarding the functional form of the unknown quantities. In addition, only one iteration is necessary for calculation, and no initial guess is required.