Recent solar inverter there is an increasing demand for high efficiency and economy. The alternative can be applied to the transformer-less type grid-connected inverter. In general, transformer-less grid-connected inverter to operate input side solar module connected floating. Due to that ground voltage raises between solar module and ground. As a result, it accelerates the PID(Potential Induced Degradation) phenomenon and thereby causes a risk of electric shock and if not inhibits the efficiency of photovoltaic solar modules. This paper proposed ground detect technique and switching technique which reduce ground voltage between solar modules and ground in transformer-less type grid connected inverter system. The proposed control method and technique was verified through the simulation results and experiment, using the Power SIM.