The present invention discloses a light emitting diode (LED) lens, a back light module and a liquid crystal display (LCD) device. A LED lens is of a direct type back light module; the dispersion index of said LED lens is less than 0.1; said dispersion index is: k dispersion = ∫ A  ∑ i   d i d total    A ; dA is a microfacet of the main luminous surface of the LED blue chip; di is a solid angle of the incident angle which is just in the critical area when dA light is reflected to the lens; the critical area refers to an area in which light with different wavelengths emitted by the LED is dispersed in the lens; the total solid angle of color separation corresponding to microfacet dA is: ∑ i   d i ; dtotal is the solid angle of the lens light emergent surface corresponding to any microfacet. The present invention can avoid dispersion phenomenon under the condition of guaranteeing wide luminance.