This paper studies the measuring method of fluorescence lifetime for the high-lying triplet state of Na2. The response function influence on the measuring apparatus has been eliminated effectively by simulating the equifrequent two-photon excitation process with the frequency doubler and numerically calculating the convolution of the fluorescence decay curve. Then, the fluorescence lifetime of the high-lying triplet state 23Πg-a3 Σu+ in Na2 has been measured.