Abstract: Considering the serious time-delay and rough detection of pH by operators，a soft sensor of pH based on machine vision is presented.Froth color，size and velocity are selected as the most relative features with pH.Furthermore，the initial structure of fuzzy system is given using subtractive clustering.The correlation of image features and pH is described using membership function.Parameters are optimized by using variable metric hierarchy chaos algorithm.The soft sensor model based on fuzzy neural network is set up.The results show that the proposed model performs well detection precision online.