The NO concentration of turbulent jet flames with different fuel, jet velocity, and jet diameter are simulated with the turbulent NO reaction time model. The predicted NO profile has very good agreement with the experimental data. Each flame has an optimal model constant C value. By comparing the flames with different operation condition and fuel, it is found out that the C value is insensitive to the operation condition such as jet velocity and jet diameter. The C value is mainly determined by fuel, its diffusion and reaction characteristics. The faster the fuel and air mix and react, the larger the C value. The fuel/N₂ mass diffusion coefficient is chosen to represent fuel's diffusion characteristic, and the flame speed of stoichiomatric fuel/air mixture is chosen to represent fuel's reaction characteristic. From the data of the six flames, accurate correlations among model constant C, mass diffusion coefficient, and flame speed are established.