Experimental results on fire and predictive results by simulation can commonly be expressed with a curve related to time. To quantitatively determine the consistency of the two curves, method of functional analysis is introduced to analyze the errors between them. The process of fire in a close space is numerically simulated by large eddy simulation with Smagorinsky subgrid-scale model; this simulation adopts Navier-Stokes equations to describe the transport of smoke and heat, which is suitable for compressible flow with low Mach number. The calculation result shows that the method of functional analysis can be used to describe the errors between the two curves, norm is a measure of the relative errors between them, and cosine is a quantitative measure of similarity in curve shape.