The invention provides a current amplifier. A D/A signal is sent to a control IC module; the control IC module forms a sine pulse width modulation waveform SPWM; the pulse width modulation waveform issplit into four paths and respectively supplied to four bridge arms of the full-bridge switch group to control the output waveform, the output current is sampled by the current sampling module and then is collected to the control IC module, and a PID adjustment mode is adopted to form a feedback loop, so that the stability of the output current is ensured.