Conventionally Peltier device has been controlled precisely by pulse driving current. In this study, it is shown that driving Peltier device by DC current controlled by pulse signal increases COP of cooling system with reducing self-heating in the device keeping accurate controlling. In practical application, the DC current driving can be achieved easily by connecting one electric condenser with large capacitance to the Peltier device in parallel. In results of analysis for electric circuit, the DC driving current reduced the self-heating in the Peltier device to conventional calorific power multiplied by driving duty-cycle value. Heat absorption rate in the Peltier device was increased by half of the reduction in the self-heating. Thermal equivalent circuit of Peltier device considered Seebeck effect was proposed to analyzed COP accurately. It was also analyzed COP of system driven by each current by using proposed thermal equivalent circuit. In result of experiment, it was possible to confirm that COP in cooling system using the DC driving current was increased than conventional system. In particular, the COP increased to equal or more than 2.01 times in less than 50% of driving duty cycle.