Research is performed on the light-weight four-principle-elements high-entropy alloys, an AlxCrFeMn (x=0.5, 1, 2, 3, 4) system, in an attempt to study the phases and microstructures. The compositions of this alloy system are designed by the CALculation and PHAse Diagrams (CALPHAD). Experimentally, X-ray diffraction (XRD), synchrotron diffraction, scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) have been implemented to characterize the phases and microstructures. According to the experimental results, in the as-cast state as the content of Al increases, laves phases appear in the disordered body-center cubic (BCC) solid solution phase, which may lower the ductility of the alloys. Transmission electron microscope (TEM) will be used to verify the compositions of the laves phases. After microstructural characterization, compression, tension, and four-point bending fatigue will be applied to study the mechanical properties of the AlxCrFeMn alloys.