To overcome the limitations of the ionization chamber-based tritium monitor, a design for a multichannel plastic scintillator-based detection chamber for monitoring tritium in air is proposed. The performance of the chamber was characterized by Monte Carlo-based calculations with various design parameters such as thickness of the plastic scintillator (t) and number of channels (n). We considered the volume and detection efficiency of the chamber to evaluate the performance of the detector. The expected counting rate curve was in good agreement with the expected simplified physical model. The minimum detectable activity (MDA) was shown at t = 0.5 mm and n = 48 and estimated to be 29.9 kBq/m3. Compared with the experimentally estimated MDA, the relative difference was approximately 24%. However, this difference is understandable considering the different lower level of discrimination and light loss during transportation assumed in the model. The proposed tritium detection chamber is expected to be useful for environmental monitoring at some level as well as for monitoring of tritium leaks from fusion or CANada Deuterium Uranium (CANDU)-type reactors.