A heat engine model of a sing particle confined in a one-dimensional harmonic trap is established. The model, as a quantum-mechanical analog of the Carnot engine, does work to outside when both the width of the potential and the quantum state change very slowly. On the assumption that the width of the potential moves at a very slow speed and the heat leakage is included, we derive the general expressions for several performance parameters, such as work, power output, efficiency, etc. We find the optimally operating regions and the optimal values of performance parameters of the heat engine cycle.