Considering the process high dimensionality, multi-operation, time-variant characteristics, and unknown mode duration, it is challenging to conduct the statistical analysis and online monitoring for multi-mode processes. The process monitoring model based on the Gaussian mixture model(GMM) combining quantitative with qualitative information solves several key points, such as mode classification of offline data, model building for stable modes and transitional modes, and mode identification of online data. Process monitoring for multi-mode processes is realized by using the proposed method.