 The Ionic liquid compressor has been developed as a new and promising compression technology for hydrogen gas. It inherits the advantages of both the Ionic liquid and the hydraulic system. The liquid density is one of the key parameters influencing the fluid flow field, the sloshing of the bulk liquid, and the movement of droplets generated during the compressor operation. An appropriate selection of the liquid density is important for the compressor design, which would improve its thermodynamic performance. However, the density of the Ionic liquid varies significantly depending on the specific combination of the cations and anions. To address this issue, this paper proposes a methodology to select the optimal liquid density used in the Ionic liquid compressor for hydrogen storage. Numerical simulations were conducted to analyze the gas-liquid interaction in the compression chamber under various liquid densities. Results showed that increasing the liquid density promoted the detachment of the Ionic liquid from the cylinder cover during the suction procedure and the contact of the bulk liquid on the compressor cover when the gas is compressed in the cylinder during the compression procedure. Additionally, the droplet size and the dimension of the derived gas vortex decreased. This article was authored by Igua, Chiwang, Mao Faking, and others. We are article.tv, links in the description below.