The invention provides an isothermal compressor performance test calculation method. The method comprises the steps that step 1, parameters of an isothermal compressor are collected; step 2, multivariable numbers in a calculation process are preliminarily determined, specifically, in step 201, inlet and outlet pressure and temperature parameters of all stages of the design
modal are obtained, in step 202, the multivariable numbers of all stages of the design
modal are calculated, in step 203, the multivariable numbers of all stages of the test
modal are preliminarily determined, specifically,the multivariable numbers of all stages of the test modal are made to be equal to the multivariable numbers of all stages of the design modal; step 3,
test data are preliminarily calculated; step 4, data comparison and
correlation coefficient selection iterative calculation are performed, specifically, the complete
machine power N calculated in the step 3 is compared with the actually measured power N, a correlation power adjustment coefficient is calculated, the multivariable numbers of all stages are recomputed, specifically, the multivariable numbers of all stages of the test modal are re-determined, the multivariable numbers of all stages of the test modal are made to be equal to the multivariable numbers of all stages obtained by re-calculation, and the calculations in the step 3 andthe step 4 are repeatedly iterated; and step 5, correlation property parameters are calculated.