As new luminescent nanomaterials, carbon dots have superior properties regarding their multi-color emission, chemical stability and biocompatibility, which are important for potential biological and medicine applications. Tuning the photoluminescence of carbon dots using hydroxyl radical through fast chemical reaction can be a simple and cost-effective method to modify their optical properties. Carbon dots of red fluorescence (r-CDs) were first prepared from phenylenediamines by a solvothermal method and subsequently treated with hydroxyl radicals or tert-butyl peroxyl radicals to generate carbon dots with new emission properties. Instead, other reactive oxygen such as singlet oxygen and hypochlorite could mainly quench the fluorescence of the r-CDs. With further investigation, it was found that these oxygen radicals played roles like chemical scissors cutting the surface chain groups of r-CDs to smaller-sized CDs, resulting in blueshift of emission. These findings may be helpful to investigate the mechanism relating to fluorescence properties of carbon dots, and it also provides a new method to control the emission of carbon dots through simple chemical treatment.