The present invention provides square seal, a manufacture method of square seal and a manufacture method of a backlight module. The square seal utilizes the roulette design. As being assembled, the redundant material outside the roulette is removed along the roulette to obtain the square seal of narrow frame so that the square seal achieves the narrow frame without the issues of overflow seal and waste material adhesion. The square seal can be easily separated from the waste material to effectively reduce the defect rate. In the manufacture method of the square seal according to the present invention, the square seal inner frame line is first cut on the seal body film material, and then the dotted roulette is formed at position of the square seal outer frame line is pre formed, and finally, the circle of the square seal reserved outer frame line is cut at the periphery of the roulette.