Active light manipulation plays a critical role in nanophotonics. In this Letter, we investigate the modulation properties of magnetic dipole (MD) emission based on the phase change material Ge2Sb2Te5 hollow nanodisk (GST-HND). The results show that the amorphous GST-HND supports a strong MD response with a radiative decay enhancement of 282 times and quantum efficiency of 100%. More importantly, by tuning the crystallization rate of GST, the active manipulation of MD radiation is achieved with a quantum efficiency modulation depth of up to 95% at a specific wavelength. Our work may provide significant instruction for the active tuning of optical nanodevices.