The invention relates to a method for determining copious cooling medium liquid level in space propulsion and belongs to the technical field of spaceflight testing. According to the method, a coaxial capacitive sensor installed in a copious cooling medium storage tank, a transmission circuit located outside the storage tank and a signal connecting line connected with the sensor and the transmission circuit are included. The coaxial capacitive sensor comprises a metal inner pipe and a metal outer pipe which are arranged in the liquid level change direction, are kept coaxial and are at fixed intervals. The signal connecting line is formed by an inner conductor, a middle conductor and an outer conductor. The signal transmission circuit is composed of a signal source with a public reference point, an impedance transformer for eliminating influences of a connecting line attached capacitor and a detecting unit for outputting response liquid level height variation. According to the method, it is guaranteed that a linear relation between sensor capacitance in space propulsion application and liquid level height is established, measurement accuracy is improved, and the number, space and weight of cables led out and arranged are saved.