[Aim]  To clarify the population dynamics patterns of Grapholita molesta in Changli, Hebei Province, and to optimize the size of insect-proof mesh to protect orchard fruits from this pest. [Methods]  Pheromone traps were hung at 1, 2, 3, 4 and 5 m heights in the insect-proof screens during 2018-2019 in experimental orchards at the Changli Fruit Research Station, Hebei Academy of Agricultural and Forestry Sciences. Both inside, and outside, enclosures screened with insect-proof mesh of different sizes, and the number of insects captured was recorded and compared. Population dynamics and the rate of fruit decay were investigated by setting different combinations of purse seine and top nets with different sized mesh to identify the optimal mesh size. [Results]  More G. molesta were caught in traps set at 2 m. Compared to the unscreened area, the number of G. molesta and rate of fruit decay were significantly reduced (df=16, F=13.360, P≤0.001; df=16, F=7.817, P≤0.05) within the screened areas. A mesh size of 0.3 cm×0.3 cm reduced the number of G. molesta captured annually from 150 to 40 per trap, and the fruit decay rate from 70.0% to 15.9%. There was no obvious difference between areas screened with the same mesh size, but different top mesh size (df=6, F=1.818, P=0.069). [Conclusion]  Most adult G. molesta in pear orchards fly at a height of about 2 m. Although the size of the top mesh had no significant effect on the number of G. molesta trapped, it plays an important role in preventing damage from hail and birds. Insect-proof mesh of 0.3 cm×0.3 cm with a top mesh size of 2.0 cm×2.0 cm is the most cost-effective choice for reducing damage to orchard fruits from G. molesta.