Introduction To evaluate the 6-month efficacy and safety of 650 nm low-level red light (LLRL) for myopia control in children. Methods This was a single-center, single-masked randomized controlled trial. A total of 224 children aged 6-12 years with spherical equivalent error (SER) of - 6 diopter (D) to - 0.5 D were enrolled, and were randomized to LLRL group or control group. Children in the LLRL group underwent treatment twice daily, each lasting for 3 min, there was an interval of at least 4 h between treatments. Children in both groups were allowed to wear single-vision spectacles; no additional intervention was given to the control. The primary outcomes included change in cycloplegic SER and change in axial length (AL) during 6 months. Results The median 6-month changes in AL of the LLRL and control groups were - 0.06 mm (interquartile range, IQR - 0.15, 0) and 0.14 mm (IQR 0.07, 0.22), respectively. The difference between groups was significant (Z = 10.021, p < 0.001). The median 6-month changes in SER were 0.125 D (IQR 0, 0.375) and - 0.25 D (IQR - 0.5, 0) for the LLRL and control groups, respectively. The difference between groups was significant (Z = 8.827, p < 0.001). Compared with the control, the proportion of children with hyperopic shift in the LLRL group was higher (51.65% vs. 3.41%, p < 0.001), and the proportion of children with shortened AL in the LLRL group was higher (63.74% vs. 2.27%, p < 0.001). No adverse event was observed. Conclusion 650 nm LLRL significantly slowed down the myopia progression in children aged 6-12 years, and there was no observable side effect in the short term.