A closed-loop brain stimulation apparatus and a method for generating a stimulation voltage thereof are provided. The closed-loop brain stimulation apparatus includes a brain signal receiving apparatus, a controller and a stimulation voltage generator. The brain signal receiving apparatus receives a plurality of brain signals. The controller performs phase correlation operations on the brain signals during a plurality continuous time periods respectively for obtaining a plurality of phase operation values, and generates a stimulation enable signal according to the phase operation values. The stimulation voltage generator generates a stimulation voltage according to the stimulation enable signal, and transports the stimulation voltage to an electrode pair.
