Because of having better corrosion resistance properties than crystalline uranium alloys, U-based metallic glasses show strong potential of applications in nuclear fields. U-Co and U-Fe are U-based important base glass systems, from which almost all the reported multi-component U-based amorphous alloys derive. However, which system possessing higher glass forming ability is unclear yet. Therefore, the relationship between the glass formation and the solidification rate is studied on two glassy alloys U_66.7Co_33.3 and U_69.2Fe_30.8 in this work, which are the best glass former in the corresponding system. A series of amorphous samples were prepared by modifying the cooling rate of their melts, and then were measured by using XRD and calorimetric analysis technique. The results show that both alloys were able to nearly amorphize completely at higher cooling rate, and tended to segregate U₆Mn-typed crystalline phase when the cooling rate declined to some extent. In contrast, the U-Fe alloy needs a much lower critical cooling rate to achieve fully amorphous structure, directly demonstrating that U-Fe system possesses stronger glass forming capacity than U-Co. The reason for this conclusion is that the former system is of both thermodynamic and kinetic advantages for glass formation. This result can be applied as the foundation to exploit superior novel multicomponent U-based amorphous alloys.