Tremor with a roughly sinusoidal profile usually occurs in the upper limb and affects the individuals' living activities. Functional electrical stimulation (FES) system is intensively studied to suppress tremor without interfering voluntary movement. In this paper, we propose a programmable stimulator to output electrical pulse modulated by the real-time feedback. Meanwhile, this stimulator with two channels is used to stimulate a pair of antagonistic muscles in the upper limb. Based on the analysis of the human skin impedance, the hardware and software of the stimulator is designed. It is noted that the stimulation pattern could be modulated by the controller via the Bluetooth for the miniaturization and portability. The experimental results demonstrated that the stimulator could provide the expected electric pulse with the amplitude modulation and pulse width modulation. Furthermore, the elbow joint angle obtained by stimulating the biceps muscle or triceps muscles with different frequency/amplitude shows that the stimulator could be used to activate the muscles in order to suppress tremor or restore the function of pathological limbs.