In this paper, a simple introduction about the interpolation method and the parallel algorithms is given, and Lagrange interpolation is carried out and applied in accordance with the idea of the parallel, analysing the developments and principles of the parallel, giving the application that the parallel algorithm is used in the Lagrange interpolation, then the parallel algorithms' advantages are showed in the numerical analysis according to the speedup ratio and efficiency. After careful scrutiny, parallel algorithm is applied to the interpolation reduces the time greatly, further, the fields of the parallel algorithm and Lagrange interpolation in practical applications are expanded. Finally it is applied to the low humidity dew point detection area with low humidity environment. The parallel Lagrange interpolation method is studied in the non-linear relationship which is shown by the measure of the capacitive sensors frequency and dew-point values.