A method of preparing quantum dots and the quantum dots are provided. The quantum dots are doped with manganese ions and various kinds of halogen ions such that when the quantum dots emit light, they will have a dual luminescence system, one is intrinsic luminescence of perovskite quantum dots and the other is doping luminescence of the manganese ions. The intrinsic luminescence of perovskite is adjustable from 410 nm to 520 nm based on the ratio of the amounts of different substances having various halide ions, which increases the wavelength range of a quantum dot luminescence spectrum so that the application scenario of the quantum dots is wider.