A direct method is developed for determining the wall heat flux in film condensation on a horizontal elliptical tube. A finite-difference method is employed to discretize the condensation domain, and then a linear inverse model is constructed to identify the unknown conditions. The inverse analysis is based on the assumption that the film thickness measurements are available over the domain. Our approach is to rearrange the matrix forms of the differential governing equation and estimate the unknown surface conditions. Then, the linear least-squares method is adopted to find the solution. For condensation problem, the governing equation is non-linear. The present woke proposes a transformed treatment for solving both inverse and direct problems. In contrast to the traditional approach, the advantage of this method in inverse analysis is that no prior information is needed on the functional form of the unknown quantities, no initial guess is required and the iterations of calculation process need be done only once. Finally, the effects of measurement errors, sensor positions and the measurement points on the inverse solutions are discussed.