The invention relates to a light mixer and a backlight module which comprises the light mixer. The backlight module comprises a plurality of light mixers and a diffusion layer; each light mixer comprises a light mixing plate where a plurality of diffusion particles are mixed, a plurality of lumination sources, a plurality of upper reflection layers, a lower reflection layer and a half-permeable layer; the light mixing plate is provided with an upper surface, a lower surface, peripheral surfaces and a plurality of receiving holes; furthermore, the material of the light mixing plate is providedwith a first refractive index; the diffusion particle is provided with a second refractive index; the difference of the second refractive index and the first refractive index is 0.01 to 2.00; the lumination source is respectively arranged inside the receiving holes; the upper reflection layers are respectively arranged right above the lumination source; the lower lumination layer is arranged on the lower surface of the light mixing plate; the half-permeable layer enwraps the peripheral surfaces of the light mixing plate; the diffusion layer is arranged above the light mixer; therefore, the backlight module has simple process, low manufacture cost and simple and convenient maintenance.