Oxidation of cellulosic fibers by the TEMPO system is highly efficient for obtaining micro/nano-sized fibrils. In this study, the dissolution degree related to the yield of products has been firstly and deeply investigated with treating bamboo pulps under various process conditions. Moreover, the dissolution behavior and mechanism for revealing the “phase transition” process of cellulosic fibers have been also studied. From the kinetic behavior results, it was found that the end dissolution degree of original pulps is almost fully controlled by the time-dependent TEMPO and especially NaOCl concentration. Meanwhile, the NaBr dosage and process temperature could also affect the dissolution rate. Based on the dissolution data, a two-stage dissolution kinetic model was firstly presented. According to the model, the difficulty of the dissolution process was evaluated.