The invention provides a 18650 lithium ion battery pack structure, which includes: lithium ion battery individuals, a bottom plate, a side plate, a pressure plate, a cover plate, an electrical connector fixing plate, an elastic plate, an electrical connector, a guide bar, and a grounding device, and is characterized in that the positive electrodes of all the lithium ion battery individuals have the same orientation so as to contribute to modular expansion; the lithium ion battery individuals are directly bonded in the sleeve-type bottom plate so as to achieve rapid heat transfer; sufficient gaps are arranged between the lithium ion battery individuals to release the stress generated during the cyclic process of the lithium ion battery individuals; the elastic plate is arranged between thelithium ion battery individuals and the pressure plate; by adjusting the amount of deformation of the elastic plate, the lithium ion battery individuals and the bottom plate can be tightly connected;the high-resistance grounding device can release the charges accumulated in the battery pack structure. The structure provided by the invention has high specific energy, good thermal conductivity, high structural strength, and good safety and reliability, and is suitable for the field of small satellites.