The invention relates to a portable tool for a closing spring. The portable tool comprises a rack; a pressing cylinder that can slide vertically at a vertical plane is arranged at the rack; and a connecting end of the pressing cylinder and the rack is driven by a drive mechanism to make vertical reciprocating motion. The pressing cylinder includes a cylinder body for pressing and supporting a pressing plate of a closing spring of a circuit breaker; an avoidance port through which a pressing plate nut of the closing spring of the circuit breaker passing is formed in the tail end of the cylinder body; and a notch is formed in the peripheral part of the cylinder. The tool has a simple structure; and an opening spring of a circuit breaker can be dismounted or mounted conveniently when only one person carries out operation. The tool can be carried conveniently; the labor force is reduced during the operation; and the manpower and time are saved.