The invention discloses an internal structure of soft package lithium ion battery, which comprises a housing and a battery equipped in the housing, and EVA is equipped between tabs, and the tab of the battery is provided with a PCB board with through hole, and the tab crosses the PCB board. The invention can guarantee good contact of tab after the electrical core is connected in series connection, and simultaneously guarantee non-falling after welding, and the slit between electrical core tabs can be filled with insulated EVC with high temperature resistance and good formability, and the EVA is a plastic material which is composed of ethene (E) and vinyl acetate (VA). Ultrasonic welding of tab can play the role for reducing internal resistance between insulators and preventing falling caused by unfirm fixing of tab. After welding, scolding tin for tab can play the role for reinforcing soundness of the tab, and simultaneously facilitating link of wire harness. The tab crosses PCB with through hole, thereby reinforcing fixation of tab and increasing anti-compression property of electrical core tab position.