Abstract: Several isotopes of xenon are sufficiently produced in fission and a few of them have suitable half-lives and radiation to be detected. These are ¹³¹Xe^m, ¹³³Xe, ¹³³Xe^m and ¹³⁵Xe and they have been selected for continuous monitoring in CTBTO international monitoring system. Employing the phoswich technology with β-γ coincidence counting capability accompanied by digital signal processing of PMT pulse, the current coincidence detectors were simplified. The radiation transport simulations were performed using MCNP toolkit to determine the optimum design and estimate the detection efficiency of the β and γ rays in phoswich detector. The results show that almost all of the beta particles deposite in plastic scintillator BC404 as its thickness is set to 1.5 mm. The self-absorption of radioxenon sample was also observed. The absorption of 346 keV β ray increases by 45.6% as the pressure from 0.1 MPa to 0.25 MPa. The data acquisition and analysis system was developed as the phoswich detector for radioxenon detection was constructed recently. The preliminary experiments demonstrate that the phoswich detector is efficient in reducing the background and the inhibiting factor is about 96.4±1.0.