Abstract: The type and operation of smokescreen were described, the masking principle of jet smokescreen was analyzed .According to the three-primary-color principle, a measurement utilizing red-green-blue (RGB) color mode to assess the chroma of color smokescreen was presented. The attenuation rate data matrix difference method which was currently widely-used to measure the forming time of smokescreen and its errors were analyzed, and a new method using color smokescreen RGB data matrix was proposed to measure the forming time of color smokescreen. The method can eliminate the systematic errors caused by the factors such as the shape and forming way of smokescreen , the target amount, the disposition pattern and so on .Analysis result shows that the measurement accuracy of the method for jet smoke formation time improves 90%, which has the advantages of high accuracy and easy data processing, and provides an effective measure for the smokescreen shielding effect assessment.