The invention relates to the technical field of display, in particular to a backlight source, a preparation method thereof and a backlight module. A point light source is converted into a surface light source, and meanwhile, color offset caused by the fact that incident light rays from one side away from a circuit substrate excites a fluorescent layer again is avoided. The backlight source comprises the circuit substrate and multiple LEDs (light emitting diodes) arranged on the circuit substrate, wherein a gap is reserved between every two adjacent LEDs, and a reflecting layer is arranged on the circuit substrate between any two adjacent LEDs; each LED comprises a light emitting chip and a fluorescent layer arranged on the light emitting side of the light emitting chip, and the light emitting direction of the light emitting chip faces one side away from the circuit substrate; the backlight source further comprises a light ray blocking structure arranged on the light emitting sides of the LEDs, and the light ray blocking structure is used for reflecting light emitted by the LEDs to the reflecting layers, emitting the light after the light is reflected by the reflecting layers and blocking incident light rays from one side away from the circuit substrate, so that the light rays are prevented from illuminating the fluorescent layers.