The HUST Ku-band aperture synthesis radiometer (ASR) is a 16-channel thinned array MMW imaging radiometer. Phase and amplitude calibration of MMW ASR is a crucial problem. A simple and effective calibration approach, which makes use of single external source in a known location, is proposed to tackle this problem in this paper. By the external noise source, the approach allows online estimation of the correct values of the ASR array phase and amplitude, without cost of special calibration hardware. Initial experiment images suitable for demonstration of calibration are present. All results show that phase and amplitude calibration is sufficiently accurate to satisfy for the MMW aperture synthesis radiometer requirements.