Objective To explore the changing trends and risk factors of nosocomial infection of very low birth weight and extremely low birth weight preterm infants in five years. Methods There were 303 cases of very low birth weight and extremely low birth weight preterm infants admitted to the neonatal intensive care unit of Affiliated Jiangmen Hospital of Sun Yat-Sen University, Guangdong Province, from January 2014 to December 2018. The infection rate, infection times rate, incidence of infectious diseases, clinical characteristics of the infected and non-infected groups, changes of pathogens and drug-resistance bacteria, and risk factors were retrospectively analyzed. Results There was no statistical difference in the infection rate, infection times rate, and incidence of infectious disease of preterm infants in five years (P < 0.05). Comparison of clinical characteristics of preterm infants with nosocomial infection in five years: parenteral nutrition (PN) time and peripherally inserted central catheter (PICC) time in the last two years were longer than in the first three years (P < 0.05); the application rate of the third generation cephalosporin after birth in 2017 was higher than that in 2014 (P < 0.05), and the rate in 2018 was higher than those in 2014, 2015 and 2016 (P < 0.05). Comparison of clinical characteristics of preterm infants without nosocomial infection: Gestational age in 2016 was smaller than those in 2015 and 2017 (P < 0.05), and that in 2018 was smaller than that in 2017 (P < 0.05); the rate of invasive ventilation in 2016 was higher than those in 2014, 2015 and 2018 (P < 0.05); intubation time in 2016 was longer than the other four years (P < 0.05); the application rate of the third generation cephalosporin after birth in the last three years were higher than those in the first two years (P < 0.05). Compared to 2014, 2017, and 2018, the rate of umbilical venous catheter (UVC) in 2016 had an increase (P < 0.05). In the past five years, Klebsiella pneumoniae and Escherichia coli were still the most common pathogens of nosocomial infection in preterm infants. The proportion of pathogens was statistical difference in human Staphylococcus, which increased in 2018 compared with the previous four years (P < 0.05). Comparison between the infected group and the non-infected group showed statistical differences in terms of gender, birth weight, gestational age, tracheal intubation, UVC, PICC and application of the third generation cephalosporin after birth (P < 0.05). Tracheal intubation time, PICC time, PN and hospitalization time in the infected group were all longer than those in the non-infected group (P < 0.05), and albumin level was lower than that in the non-infected group (P < 0.05). Logistic regression analysis showed that birth weight lower than 1000 g, tracheal intubation, tracheal intubation time and PICC time were independent risk factors for nosocomial infection in very low birth weight and extremely low birth weight preterm infants. Conclusion The infection rate of preterm infants in hospitals has not decreased in recent years. Less gestational age, reduced invasive ventilation support, and shorter tracheal intubation time were the characteristics of preterm infants without nosocomial infection in the last two years. But application rate of the third generation cephalosporin increased. Improving the birth weight, reducing tracheal intubation, shortening the time of tracheal intubation, and PICC can reduce the incidence of nosocomial infection in preterm infants.