The invention discloses a test device and method for measuring a single photon beam polarization state in real time. The device comprises a test system and a calibrating system, wherein the test device divides a tested light beam into four beams by utilizing an energy spectroscope and a phase spectroscope, and an input signal is detected respectively by four single photon detectors. A calibratingdevice obtains an optimal instrument matrix of a system; and when in test, the stokes vector of the tested signal can be obtained according to the instrument matrix and a test signal. The invention has the advantages that the system has no rotating part and has high test speed; the test system fully utilizes the energy of the test light beam and can be used for the polarization state detection ofa single photon or an extremely weak light beam; and the system is provided with a variable phase compensator, can obtain an optimal system instrument matrix and has high test precision and reliable result.