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As a part of the development of the large high pressure liquid oxygen/liquid hydrogen (LOX/H (sub 2) ) engine (LE-7) of the large launch vehicle H-II, to evaluate the performance of large flow rate high delivery pressure cryogenic pumps, an efficiency and head similar to a polytropic efficiency and head for gas compressors were proposed as the evaluation index of pumps for compressible hydrogen. The defined efficiency and head were obtained by accumulating adiabatic heads between two isobars in close proximity to each other in a compression stroke, under the assumption, liquid was compressed at an equal adiabatic efficiency in the region between two isobars. As the relation among delivery pressure, the number of isobars and the difference between the adiabatic and defined efficiency was calculated, there were extremely large efficiency differences in liquid hydrogen. The defined efficiency and head were fairly close to the test data of the LE-7 cryogenic pumps. 9 refs., 11 figs., 2 tabs.