To realize online measurement of tritium production rate in a strong gamma field environment, we developed a compact back-to-back ⁶Li/⁷Li glass detector. The size of each lithium glass scintillator is 3.0 mm×3.0 mm×0.4 mm. Titanium dioxide with a thickness of 0.5 mm acts as a reflective layer between and on the side of the scintillators. The whole volume of the detector is 4.0 mm×4.0 mm×1.3 mm, which ensures that gamma rays of the two scintillators are almost the same and realizes simultaneous measurement of the gamma rays. The gamma signal produced by the ⁷Li glass detector is used as the gamma background deduction of the ⁶Li glass detector. Pulse height spectra of the two lithium glass scintillators irradiated by ⁶⁰Co gamma are almost the same, which verifies the consistency of gamma signals of the two scintillators. The pulse amplitude spectrum were measured at the thermal neutron channel of the reactor and under the direct irradiation of ²⁵²Cf, the signal-to-noise ratio of neutron gamma obtained are both greater than 1, which can effectively deduct the gamma background. The above experiments show that the developed small lithium glass detector can effectively discriminate the gamma rays under strong gamma environment, and is used for on-line measurement of tritium production in the simulated blanket of fusion-fission hybrid reactor.