The subthalamic nucleus (STN) is the only excitatory glutamatergic nucleus in the basal ganglia circuitry. It not only is a key node in the classical indirect pathway, but also forms the" hyperdirect" pathway directly connecting the cortex, and even is implicated as a pacemaker for activity of whole basal ganglia. Due to the key position of STN in the basal ganglia circuitry, the STN is an optimal target for deep brain stimulation (DBS) in the neurosurgical treatment of Parkinson's disease (PD). However, the therapeutic mechanisms underlying the amelioration of parkinsonian motor dysfunctions induced by DBS on STN remain enigmatic. This paper reviews recent progresses in the studies on the input-output configurations and functions of STN in the basal ganglia circuitry, and summarizes the hypotheses for mechanisms of DBS for the treatment of motor dysfunctions in PD. Studying on the DBS mechanisms will not only help to develop strategies for treatment of PD, but also contribute to the understanding of functions of the basal ganglia circuitry.