The invention relates to automobile parts, and discloses a fuel tank cap lock for a car. The fuel tank cap lock for the car comprises a lock cylinder component (1), wherein a locking component (3) is arranged on the lock cylinder component (1), the locking component (3) comprises a locking ratchet wheel (301), a locking paw (302), a lock sleeve (304) and a reset torsional spring (303), at least one boss (3011) is arranged on the locking ratchet wheel (301), the locking paw (302) attaches to the boss (3011), the locking paw (302) is arranged in the lock sleeve (304), a fixture block (3041) is arranged on the lock sleeve (304), and the lock sleeve (304) is further internally provided with the reset torsional spring (303); when the fixture block (3041) and the locking paw (302) are clamped, the lock cylinder component (1) is unlocked, when the locking ratchet wheel (301) rotationally pushes the locking paw (302), the reset torsional spring (303) drives the fixture block (3041) to break away from the locking paw (302), and the fixture block (3041) drives the lock cylinder component (1) to rotate through the lock sleeve (304). The fuel tank cap lock for the car has the effects of being convenient to use, and being capable of automatically locking, and lowering potential safety hazards.