Thermonuclear reaction rate describing thermonuclear burning efficiency in thermonuclear fusion is studied.As one species atomic nucleus with Maxwell velocity distribution,another species atomic nucleus velocity is divided into several groups.Velocity group thermonuclear reaction rate and averaged thermonuclear reaction rate are deduced,and simulation codes are obtained.Taking deuterium-tritium thermonuclear fusion reaction as an example,velocity group thermonuclear reaction rates and corresponding averaged thermonuclear reaction rates are calculated and analyzed comparing with exact direct integration results.Finally,relation between averaged thermonuclear reaction rate and velocity group number is studied.