The design of this study is an experimental research design, and the research subjects who meet the conditions of acceptance will be used as randomized controlled trials. Cases meeting the sampling conditions in the neonatal intensive care unit were stratified according to birth weeks (26 to 27+6 weeks and 28 to 31+6 weeks), and then randomly assigned to experimental group A (non-nutritive sucking 5 minutes), experimental group B (non-nutritive sucking for 15 minutes) and control group (no non-nutritive sucking). The variables controlled in this study were gestational weeks, birth weight, sex, Apgar score, respirator use, and type of milk fed. The premature infants in the experimental group were given non-nutritive sucking before the first tube-feeding and the feeding volume reached 10mL/kg/day, while the control group was not given non-nutritive sucking before tube-feeding. The interventional measures adopted in this study were set as two meals a day before 17:00, and the patients were force-fed every three hours, and the time interval between the two interventional measures was every six hours (intervention measures were provided every other meal) , the measurement time, times and intervals of the two groups are the same. Experimental group A was given pacifier NNS 5 minutes before each feeding, experimental group B was given pacifier NNS 15 minutes before each feeding, while the control group was not given NNS before feeding, and the two groups were given 150 minutes after feeding (ie 30 minutes before the next force-feeding) to monitor gastric residual volume, changes in abdominal circumference, and vomiting. Since FI mainly occurred 48-72 hours after the start of feeding, the duration of this study was 3 consecutive days to compare with the control group. The acceptance conditions of the research objects are: 1. Premature infants whose gestational age is more than 26 weeks (inclusive) to less than 32 weeks, 2. Premature neonates who have been placed with orogastric tube or nasogastric tube for force-feeding, 3. No congenital gastrointestinal tract Abnormal, 4. No serious congenital abnormalities and heart disease, no cleft lip and palate, 5. Never received stomach or intestinal surgery, 6. No central nervous system damage, 7. With the consent of their parents or guardians, and fill out the consent form By. If the condition is unstable during the course of the case, including severe hypoxemia, hypotension, esophageal perforation, necrotic enteritis, sepsis caused by infection, and grade 3-4 intraventricular hemorrhage, etc., they will be excluded.