Abstract: This paper introduces the features of the compact cyclotron CYCIAE-100 and some key physical issues in the design, including the vertical focusing of straight sector magnet structure, design of the special-shape RF resonator, space charge effect, etc. For the main magnet of CYCIAE-100, the straight sector magnet is adopted in the design to reduce the difficulties of fabricating the magnet as well as the RF cavity. Meanwhile, given the fact that the vertical focusing decreases at large radii for the straight sector magnet, the variable hill gap technology is adopted to effectively improve the vertical focusing. Space charge effect study have been carried out with the independently developed code OPAL-CYCL based on the PIC technology, and the result shows that the current limit for CYCIAE-100 is 10 mA. In-depth study results on the beam test of the machine are also described in the paper, including the tuning scheme, diagnostics device layout, beam data measured from the radial probe, and physical figures.