According to the requirement of moisture content (1%-3%) and detection precision(0.1%) for the flat gunpowder, the capacitive sensor of varied dielectric was adopted, and the system of capacitive sensor for the moisture detection of gunpowder was developed. On the basis of the analysis for temperature, moisture, mass and voltage amplitude, the multi-linear regression model of partial least-squares was established. Results show that the maximal measurement error of moisture content (0.3%-1%) is 0.12%, and the maximal error of moisture content(1%-3%) is less than 0.087%, which meeting the accuracy requirement for the moisture detection (0.1%) of gunpowder.