The present invention relates to a liquid rocket engine using a booster pump driven by an electric motor, and more particularly, to a liquid rocket engine using a booster pump driven by an electric motor in which a booster pump is installed between a propellant tank and a propellant pump so that a requirement for an inlet pressure of the propellant pump may be met even in a state in which an internal pressure of the propellant tank is reduced, resulting in reduced amount of a propellant and reduced weight of the propellant tank, and the electric motor configured to drive the booster pump may be efficiently cooled through an oxidant, a cooling line, and the like.