This paper proposes a noncontact optical measurement method based on digital speckle pattern interferometry (DSPI) to achieve precise quantification of small charges. By investigating the electric field distributions in parallelplate capacitor systems and analyzing the forces acting on charged objects, the challenge of charge measurement is converted into a problem of angular deflection detection. Leveraging the diffuse reflection characteristics of a ground glass plate, speckle patterns are captured using a CCD sensor. Through sequential grayscale conversion, Fast Fourier Transform (FFT) processing, and phase extraction algorithms, the interference fringes of speckles are reconstructed, thereby enabling noncontact charge measurement. The developed system achieves precise measurements of charges ranging from 0.1 nC to 1.0 nC under standard laboratory conditions, showing high consistency with simulation results. This work establishes a novel strategy for contactless precision measurement of small charges.