A back light module including a back plate, a light source and a bar lens is disclosed. The bar lens includes a top and a bottom center transparent surfaces, a right and a left top total internal reflection surfaces, a right and a left first emitting surfaces, a right and a left second emitting surfaces, a right and a left bottom total internal reflection surfaces and a right and a left bottom incident surfaces. The center bottom transparent surface is located between the top center transparent surface and the light source. The connecting sequence along the right of bar lens from top center transparent surface is the right top total internal reflection surface, the right first emitting surface, the right second emitting surface, right bottom total internal reflection surface, the right incident surface and the center bottom transparent surface. The connecting sequence on the left is similar to the right.