The purpose of this paper is to investigate the piston temperature and temperature distribution with varying engine torques and speeds for a farm diesel engine. This analysis is based on the concept that the piston thermal system is considered to be one part of the whole engine energy system. That is, by thermodynamics cycle simulation, the heat transfer rate from gas to metals was first calculated, and then the temperature distribution in the piston was obtained by an axi-symmetrical finite element heat conduction model. In order to verify the predicted values, input data for the cycle simulation were obtained, at the same time the piston temperature were measured. Some of the governing thermal boundary conditions of the piston were arrived at through a literature research. A comparison of computed and experimental results showed that the numerical model adequately predicts the thermal effects on the piston under various engine operation conditions.