For the developed infrared CH_4detection system based on asymmetric el lipsoid gas-cell,based on the Fick′s first law,the model on response time is established.Under the ca se of gas diffusion from the inside area to the outside area and that from the outside area to the inside area,the expressi on of the real-time concentration inside the gas-cell versus the variation time is derived,and the relations amo ng the response time,the structural parameters,the initial and final concentrations inside the gas-cell are calcul ated and analyzed.Calculation results indicate that the 10-90% response time depends on the structural paramete rs,but has no relation with the initial and final concentrations.When the long axis of the gas-cell is 7.6cm and its opening hole diameters are 0.5cm and 2.24cm,respectively,the calculated response time is about 9.42s.By usin g the fabricated asymmetric ellipsoid gas-cell and the developed CH_4detection device,the response time i s measured through experiments. When the gas concentration exchanges between 0and 10－4,the measured rise and fall times are 7.25s and 9.0s, respectively.When the gas concentration exchanges between 10－3 and 10 －2,the measured rise and fall times are both about 8.25s.The experimental results show some difference with the calcula ted results,because the experimental condition does not satisfy the requirement of the Fick′s law.Furth er,the proposed analytical theory and related models have applicative value in evaluating the response characteris tics of the detection device with structure-similar gas-cells.