A light guide plate fixing structure and a backlight module using the same, comprising a first abutting wall formed at the side edge of the light guide plate, a second abutting wall formed on the backplane, and a constant-force spring arranged between the first abutting wall and the second abutting wall; the constant-force spring has a fixing end and a support end, the fixing end being fixed on the first abutting wall, the support end forming an elastic foot that abuts against the second abutting wall, with the light guide plate being fixed with the help of the elastic force produced by bounce of the constant-force spring after being pre-compressed: when the light guide plate is expanded, it can push the spring away and be released and expanded; when the light guide plate is contracted, rebound of the spring will make the spring move with the light guide plate.