The dispersion formula of nitrogen gas at wavelengths from 0.145 μm to 2.058 μm in standard condition (temperature at 293.15 K, pressure at 101325 Pa) is deduced based on the theory of gas dispersion. A least square method is used for fitting this formula to measured data on the basis of two-order Sellmeier formula. The uncertainty of this formula in the overall spectral range is about 2.1×10-7, which is almost the same as the accuracy of the measured data. Comparing with the current dispersion formulas of nitrogen gas, the new formula presented here covers a wider spectral range, and provides more information of refractive index of nitrogen gas in 0.27～0.47 μm. The validity of the new formula has been approved by measuring the refractive index of nitrogen gas at 633 nm directly.