Three-dimensional measuring method is more fuller reflect the geometry shape message of parts pattern than 2D method. 3D parameter’s statistical property and robustness are fine. A non-contact measurement method of surface roughness 3D parameters based on digital image processing is presented. 3D surface roughness measuring system is established. In experiment, image information is gathered from the digital camera and is pre-processed by using median filtering, grayscale equalization and histogram conversion amplification. Taking five different surface roughness specimens of plain grinding for experiment, Mean value(m), Variance(σ),Root mean square deviation(Sq), Steep kurtosis (Sku) are calculated. Then the correlation between those parameters and roughness average (Ra) is analyzed. The results showed that m,σ, Sq are increasing along with Ra. But the exact correlation between Sku and Ra cannot be discovered.