The present disclosure provides a method for manufacturing a transistor having a gate with a variable work function, comprising: providing a semiconductor substrate; forming a dummy gate stack on the semiconductor substrate and performing ion implantation on an exposed area of the semiconductor substrate at both sides of the dummy gate stack to form source/drain regions; removing the dummy gate and annealing the source/drain regions; providing an atomic layer deposition reaction device; introducing a precursor source reactant into the atomic layer deposition reaction device; and controlling an environmental factor for the atomic layer deposition device to grow a work function metal layer. The present disclosure also provides a transistor having a gate with a variable work function. The present disclosure may adjust a variable work function, and may use the same material system to obtain an adjustable threshold voltage within an adjustable range.