A method for monitoring and controlling multi-phase condition of reactant in manufacturing process is provided. The monitoring and controlling method includes the following steps. A plurality of clusters of monitoring images is captured corresponding to a plurality of process reaction time points in a plurality of observation regions. According to the clusters of the monitoring images, a plurality of image index features is extracted. According to the image index features, a plurality of phase modes corresponding to the observation regions is determined. According to the image index features, a cluster of generation characteristics of the reactant corresponding to the phase modes is determined. According to the cluster of generation characteristics, an adjustment of the manufacturing process is performed.