Brassica crops infected by Plasmodiophora brassicae can produce root galls (clubroots) and be prevented from growing normally. To understand the series of changes that occur in the host root during root gall production, the resistance character of 21 Chinese cabbage lines were identified and then resistant and susceptible lines were used for infection observation. Hydroponic technology system was used for plants growing, and the infection process of P. brassicae in the roots of resistant and susceptible Chinese cabbage was examined based on morphology and microscopic characteristics using micoscope. In susceptible Chinese cabbage, the root hair infection stage occurred over approximately 7 days after inoculation, the cortical infection happened over approximatly 14 days after inoculation, and clubroots formed in approximately 30 days after inoculation. However, in resistant Chinese cabbage, the pathogen could be prevented and maintained in the root hair infection stage. This research provides a foundation for the subsequent studies of cabbage resistance of P. brassicae.