A current node correction method is proposed herein to solve the nonlinear variation of optical frequency during continuous frequency modulation of semiconductor laser sources. First, the proposed method establishes the relationship between the laser drive current nodes and the position of the minimum points of the actual beat signal; then, the current node parameters are compensated according to the position deviation between these actual minimum points and the ideal points. After several iterations, the laser frequency modulation is nonlinearly corrected. A fiber-optic frequency-modulated continuous wave laser interferometric ranging system is realized, and the linearization output of the distributed feedback semiconductor laser is obtained via the proposed current node correction method to perform a ranging experiment. The results show that the proposed method is a simple and effective calibration method, and a standard deviation below 11 μm and a linearity of 0.03% within the measurement range of 800 mm are obtained. The proposed method can be widely used for frequency-modulated continuous wave interference.