A method for manufacturing a locking arm of a carrier connecting rod includes four steps to press a metal sheet via a first stamping die and a second stamping die to form the metal sheet to include a front section, a bent middle section and a rear section. A stopper is formed to the front section, and a recessed area is formed to one side of the bent middle section. A positioning hole is defined through a center of the recessed area. A guide surface is formed to the bent middle section opposite to the recessed area. The locking arm is pivotably connected to the extendable tube of the carrier connecting rod, and the protrusion of the spring member in the extendable tube is guided by the guide surface to be retractably engaged with the positioning hole. The locking arm is manufactured at low cost and has better structural strength.