Abstract: Experiments on the ignition characteristics of polymethyl methacrylate (PMMA) slabs were conducted using a narrow-channel experimental system and a variable-pressure chamber, with ambient pressure and airflow velocity serving as the primary experimental parameters. The results indicate that the product of pressure and airflow velocity can be utilized as a coupled parameter that jointly governs the ignition delay characteristics. Specifically, when this product is below a critical threshold, the ignition delay time decreases as the product increases; conversely, it increases beyond this threshold. Under low-velocity flow conditions, the influence of ambient pressure on material ignition can be categorized into two distinct regimes: the convective heat loss-controlled regime at the material surface and the gas-phase chemical reaction-controlled regime. In the convective heat loss-controlled regime, a reduction in pressure leads to an increase in both the ignition delay time and the critical pyrolysis rate. In contrast, the opposite trend is observed within the gas-phase chemical reaction-controlled regime. Furthermore, by treating the effect of pressure as an equivalent variation in ambient oxygen concentration, a predictive model for the critical pyrolysis rate and ignition delay time under diverse environmental conditions was established. The predicted values of this model exhibit an error of less than ±20% compared with the experimental results.