BACKGROUND Extensive research has been conducted on insect chitinases. However, little is known about the function of chitinase in the regulation of the surface structure of the peritrophic matrix (PM) in larval midguts. The aim of this study was to analyze the effect of HaCHT4 on the chitin content and surface structure of the PM during larval growth and development of Helicoverpa armigera. RESULTS The expression level of HaCHT4 was lower and the chitin content was higher in the early stages of fourth to sixth instar larvae, but they were reversed in the corresponding late stages. The correlation coefficient between the expression level of HaCHT4 and the chitin content was −0.585 (P < 0.05), with a higher negative correlation of −0.934 for the fourth instar (P < 0.01). Scanning electron microscopy (SEM) showed that the surface structure of PM was multi‐laminated with small pores in the early stages of fourth to sixth instar larvae, and more and bigger pores in the late stages. Low expression of HaCHT4 caused by RNA interference (RNAi) resulted in the increase of chitin content in the PM, and the surface structure of PM became multilayered with smaller pore size in the late stage of fourth instar larvae. Also, induction of HaCHT4 by application of 2‐tridecanone (2‐TD), decreased the chitin content of PM, caused larger pores to form and lots of food bolus to attach to the PM surface, and also increased the larval susceptibility to chlorantraniliprole. CONCLUSION These results provided strong evidence that HaCHT4 plays an important role by regulating the chitin content of the PM and its surface structure, thereby affecting the sensitivity of H. armigera to chlorantraniliprole. Negative correlation between the expression profile of HaCHT4 from the midgut and the chitin content of PM in H. armigera. The effect of HaCHT4 silenced and induced on the chitin content of PM, the PM surface structure and the sensitivity of cotton bollworm to chlorantraniliprol. © 2022 Society of Chemical Industry.