The invention discloses an upper stage single machine sine scan test condition refining design method. With combination of theory and experiment, upper stage/ rocket interface acceleration of satellite and rocket load coupled analytic results is used as forcing function, the ratio of acceleration response to excitation at an upper stage system-level sine scan test single machine is used as a transmission characteristic, and the forcing function is multiplied by the transmission characteristic to obtain the maximum single machine environmental envelope. By use of the method, environmental envelopes corresponding to different frequencies can be provided so that the test condition is finer and the severity of environmental condition design is avoided, and the test condition is accurate and is with certain margin. Furthermore, the system-level sine scan test data processing and test condition envelopes can both be achieved by digital batch processing and thus the efficiency and fine degree of mechanical environmental condition design can be effectively increased.