The invention relates to a non-sealed fabry-perot cavity probe of a partial discharge optical fiber EFPI sensor. The probe comprises a sensitive diaphragm, a casing pipe, a fixed sheath, a pressure balance hole and an optical fiber. The sensitive diaphragm is installed on one end of the casing pipe. The fixed sheath is inserted into the other end of the casing pipe. The optical fiber is inserted into the fixed sheath. The optical fiber, the fixed sheath, the casing pipe and the sensitive diaphragm are connected to form a non-sealed fabry-perot cavity. The pressure balance hole is arranged in the fixed sheath and is connected with the non-sealed fabry-perot cavity. Compared with the prior art, the probe of the invention has advantages that performance is stable and so on.