Different factors that influence the alkaline degradation of cellulose in the pulping process were considered in this study. The factors were the reaction temperature, reaction time, dosage of NaOH, and metal ions. Microcrystal cellulose (MCC) was applied as the model compound. To measure the influence of different metal ions on the alkaline degradation of cellulose, K+ and Mg2+ were added into the reaction system. The Fourier transform infrared (FTIR) spectra of the MCC in the solution with and without K+ and Mg2+ were analyzed to clarify the reaction mechanism of the alkaline degradation of cellulose and MCC. Alkaline degradation increased with increasing reaction temperature, reaction time, and alkali concentration. When the reaction temperature was above 80 °C, the reaction time was above 2 h, or the alkali content was below 5 g/L, the degradation ratio of MCC decreased. The amount of degraded MCC and the concentration of glucose in the reaction solution exhibited a nearly linear relationship when the alkali quantity increased from 0 g/L to 5 g/L. K+ and Mg2+ had an opposite impact on the alkaline degradation. While the K+ promoted the alkaline degradation of cellulose, the Mg2+ inhibited it, along with an increase of the dosage of the two metal ions.