A steel cord for reinforcing pneumatic tire, is a multi-layered steel cord comprising a core, an intermediate layer and an outer layer. The core has four filaments, the intermediate layer has nine filaments, and the outer layer has fourteen filaments. At least one filament of the steel cord has a tensile strength no less than (3800- 2000xd)Mpa and d is the diameter of the filament. The twist direction of the filaments may be the same, and the ratio between the lay length of intermediate lay and the lay length of the outer lay is between 0.70 and 0.90. This steel cord achieves a good balance between tensile strength and rubber penetration, but also is cost-effective to manufacture and use.