Abstract: As the research on air temperature field in large space structure is relatively scarce,computer simulation was performed by FDS program for fire cases to study the air heating-up process for large-space structure under fire.The effect of smoke emission on fire temperature field is considered.Mathematical model of temperature field related to time has been established.The related parameters and the evaluation function of the fitting results(the square of related coefficient R₂) are obtained by a nonlinear curve-fitting method with MATLAB program.The coefficient of temperature rise velocity r and the equilibrium temperature θ_m are the main parameters related to the characteristics of space temperature field.As the value of R₂ for the heating-up curve calculated by numerical simulation and the mathematical model is more than 0.95,the mathematical model is simple,practical and credible.