The needed conditions for predicting thermal cycle of a quenching by using the finite element method have been investigated by comparing theoretical values with numerical results. The basic equation of a minimum element length for cylinder thermal cycle was proposed, which was able to calculate from informations such as an initial temperature, a radius of cylinder, a heat transfer coefficient and the aimed temperature change at the cylinder surface. The minimum time increment for guaranteeing accuracy was given against the minimum element length. It was shown that the minimum element length for pipe thermal cycle was replaced by that of cylinder. The experimental data of quenching cylinder were sufficiently predicted by the finite element method with the above minimum element length and the time increment.