Solution supersaturation ratio and crystallization pressure are the main parameters to study the crystallization failure effect of porous materials, but there are no good means to measure solution supersaturation ratio directly at present. Observations on the phenomenon of solution crystallization show that the gray scale of the image changes obviously before and after the solution crystallization, therefore, a method for measuring the supersaturation ratio and crystallization pressure of salt crystallization based on digital image processing (DIP) technology was proposed. Based on the image,the relationship between gray value and solution concentration was obtained. MATLAB software was used to draw the distribution of solution supersaturation ratio and crystallization pressure. Taking the crystallization behavior of Na2SO4 solution and NaCl solution as an example, the initial supersaturation ratios of Na2SO4 solution and NaCl solution are obtained between 1.1~1.3, and the theoretical values of Na2SO4 and NaCl crystallization pressure are calculated. The differences of the crystallization failure effect between Na2SO4 and NaCl are related to their different crystallization behaviors. The creep growth behavior of Na2SO4 crystals makes them more destructive.