CIE 1976 LAB color space coordinate is an important technical index of ZrN film, and nitrogen partial pressure has a critical effect on ZrN film color coordinate. Mid-frequency reactive magnetron sputtering is adopted to deposite ZrN layer, and through measuring the color of ZrN films and nitrogen partial pressure, the curves of CIE L*, a* and b* values of ZrN films versus nitrogen partial pressure are obtained. The results show that the curve of a* and b* values is a loop curve and L* values decrease with the rise of nitrogen partial pressure. The theoretical analysis is given by metal free-electron model. As the nitrogen partial pressure increases, the variation of color coordinate is caused by decrease of free electrons number of the films and decrease of plasma frequency. The results of X-ray diffraction (XRD) and resistivity measurement indicate that the distinct decrease of L* value at high nitrogen partial pressure is caused by that band gap of Zr3N4 is less than limit of visible light.