The present study applies a hybrid method of the Laplace transform and finite-difference methods in conjunction with the least-squares method and actual experimental temperature data inside the tested material to predict the unknown surface conditions. In the present study, the functional forms of the unknown surface conditions are unknown a priori and are assumed to be the function of time before performing the inverse calculation. In addition, the whole time domain is divided into several analysis sub-time intervals and then the unknown surface conditions on each analysis interval can be estimated. The results show that a good estimation on the unknown surface temperature or heat flux can be obtained. The effects of the dimensionless measurement time step, initial guesses, and measurement error on the estimation of the unknown surface conditions are also investigated. In order to show the validity and accuracy of the present numerical method, a comparison between the present estimates and actual experimental temperature data is made.