High-precision correction of radio wave refraction error is one of the key factors for improving the accuracy of radar detection. The accuracy of atmospheric refractive index on radar radio wave ray has a great influence on the accuracy of radio wave refraction correction. In view of the fact that the current linear interpolation method of atmospheric refractive index causes a large error in the refractive index on the radio wave ray, a piecewise atmospheric interpolation method is proposed according to the law of the variation of atmospheric refractive index, in which the linear interpolation method is used on the first section of the atmosphere, and the exponential interpolation method is employed on the second section of the atmosphere.The actual detected data of the atmospheric refractive index is used to compare the refractive indices on the radio wave ray obtained by linear interpolation and piecewise interpolation, and it is proved that the piecewise interpolation method has higher accuracy. The atmospheric refractive index obtained by the two methods is used to calculate the radio wave refraction error. It is proved that the piecewise atmospheric interpolation method can effectively improve the accuracy of radio wave refraction correction, and thus ensure the high-precision detection of the radar.