Abstract: Inverse estimation of heat source term inthree-dimensional heat conduction problem from surface temperaturemeasurements is a typical Inverse Heat Conduction Problem (IHCP). In thispaper, based on the three-dimensional (3D) numerical simulation of transientheat conduction problem with the Finite Volume Method (FVM), the 3Dtransient IHCP is generally converted into an optimization problem toinversely estimate the heat source with Adjoint Equation Method (AEM) andConjugate Gradient Method (CGM). A typical case has been shown that the twoestimation methods are feasible and not sensitive to the measurement noise.Moreover, the selection of stopping criterion for the inverse estimationalgorithm is further investigated. The results demonstrate that the closeragreement between the estimated and exact heat sources hasn't made with thedecreasing value of the objective function due to the ill-posedness of theIHCP, which can be overcome with the proper stopping criterion to simulatethe regularization effect in the IHCP.