Objective  To evaluate the changes of intraocular pressure （IOP） in myopic children undergoing overnight orthokeratology treatment. Methods  It was a retrospective case-series study. Orthokeratology was performed to correct the refractive errors of 303 eyes of 303 teenagers. The patients were divided into 3 groups： low-myopia， moderate-myopia， and high-myopia， based on the diopters. IOP， corneal curvature and refraction were taken respectively at pre-wear， l day and 7， 30， 90 days after orthokeratology. Data were analyzed by repeated-measures ANOVA tests. LSD corrections were performed to compare the differences in IOP if significant differences were found. Results  The change of IOP became stable after 1-week orthokeratology treatment， and were significant decrease in IOP after treatment （F=51.75， P＜0.01）. Moderate and high myopia had an increase of 1.04 mmHg （t=-4.81， P<0.01） and 0.58 mmHg （t=-2.65， P<0.05） respectively in IOP at 1-day visit， and low myopia only showed a downward trend at the same time （t=0.57， P>0.05）. Furthermore， the changes in diopters were positively correlated with those in IOP （r=0.131， P<0.05） 3 months post-treatment. The changes of IOP resulted by one unit change in diopter were significantly different among different degree of myopic group （F=3.57， P<0.05）. With one unit change in diopter， the low-myopia teenagers showed significantly more reduction in IOP at 0.50 mmHg than moderate-myopia teenagers （t=-2.57， P<0.01）. No significant differences were observed between low- and high-myopia groups （t=-1.86， P>0.05）， moderate- and high-myopia groups （t=0.68， P>0.05）. Conclusion  Orthokeratology results a decrease in IOP measurements. The observed patterns of IOP changes may be caused cooperatively by the changes in corneal morphology and eye accommodation function.