Traditional grid-connected inverter with isolation transformer is big, heavy, and low efficiency.Transformerless grid-connected inverter attracted more and more researchers attention due to its advantages such as small size,low cost and high efficiency. Current ripple effect is important to power loss analysis due to varying irradiation,but often be neglected.The design concept to analysis a transformerless grid-connected inverter in detailed, established a mathematical model of component loss including current ripple effect,and a test prototype has been made.