Along nucleation → crystalline growth →crystalline fraction → critical cooling rate, the relationship between the nucleation, elements, cooling rate and the Glass Forming Ability of (Cu-Zr) based glass alloys is quantitatively studied with thermodynamics method, and a better method to evaluate the critical cooling rate of glass alloys is also proposed in this paper. The computed results show that: (1) with the increase of element number, the steady state nucleation rate drops gradually. From Cu-Zr, Cu-Zr-Al, Cu-Zr-Al-Ni, to Cu-Zr-Al-Ni-Ti, the peak value of nucleation rate decreases from 1021 mol-1s-1 to 1013 mol-1s-1. It is also found the nucleation rate both drops with the substitution of Ni with Cu or Al with Zr; (2) with the increase of cooling rate, the nucleation rate drops sharply. When the cooling rate reaches 103K/s, the nucleation rates of Cu64Zr36, Cu54Zr42.5Al3.5, Cu55Zr40Al5 and Cu30Zr55Al10Ni5 drop to 109mol-1s-1, 106mol-1s-1, 107mol-1s-1 and 103mol-1s-1 accordingly.