Cationic nanocellulose materials have many desirable characteristics such as renewability, degradability, excellent adsorbability and antibacterial properties and will be expected to be used in biomedicine, antimicrobial materials and other high value-added fields, but unfortunately low efficiency of the cation of cellulose is still one of the main obstacles of the preparation of cationic nanocellulose. In this paper, carboxyethyl pretreatment was used to prepare cationic fibers instead of alkali swelling to improve the accessibility of hydroxyl groups. The effects of carboxyl content, cationic reagent dosage, NaOH amount, reaction temperature and reaction time on the cationic reaction of fibers were investigated, which aimed at optimizing the cationic reaction conditions of fibers and creating conditions for the subsequent preparation of cationic nanocellulose. The results showed that carboxyethylation could increase the degree of substitution of quaternary ammonium group and promote the cationic process of fibers. The optimal reaction conditions were as follows: the content of carboxyl group was 0.75 mmol/g, the molar ratio of cationic reagent to the glucose unit was 4:1, the amount of NaOH was 0.3 g/g, the reaction time was 5 h, and the temperature was 40 ℃. Carboxyethylation pretreatment and cationization reaction changed the length of raw fibers. The average length of raw fibers was 0.741 mm. However, the length of carboxyethylated fibers and cationic fibers were 0.642 mm and 0.588 mm, respectively. In addition, Carboxyethylation pretreatment and cationization reaction significantly improved the water retention performance of fibers, which indicated that carboxyethyl pretreatment improved the accessibility of hydroxyl groups and promoted fibers swelling performance. The water retention value of raw fibers was 1.451 g/g, and the values of carboxyethylated fibers and cationic fibers were 7.320 g/g and 9.152 g/g, respectively. Compared with alkali swelling, the cationization efficiency of carboxyethyl pretreated fiber increased by 10.62%, which proved that carboxyethyl pretreatment has a positive effect on improving the cationization reaction efficiency of the fibers.