The invention discloses a light and thin MiniLED backlight source which comprises a back plate and a light source assembly, an auxiliary marking line is arranged at the midpoint of the top end face of the back plate, through holes are further formed in the four corners of the back plate, an integrated inner cover plate is arranged in the through holes, a plurality of arc grooves are formed in the surface of the inner cover plate at equal angles, the cross section of each arc groove is of an arc structure, the four corners of the back plate are each provided with two edge grooves, the two edge grooves are perpendicularly distributed, and the through holes are formed in the inner sides of the two edge grooves. The light source assembly is composed of a backlight assembly, a light equalizing piece, a quantum dot color enhancement film, an optical thin film, a liquid crystal panel, liquid crystal and a color filter which are sequentially stacked from bottom to top. Through the designed auxiliary marking line, installation guidance can be provided for installation equipment, the precision requirement for the installation equipment is lowered, cost consumption is reduced to a certain degree, and meanwhile later manual detection can be facilitated.