The compositional design of diffusion source plays a crucial role in improving magnetic properties of Nd-Fe-B magnet. In this work, Dy80–xCexAl20 (x=0–50, in at%) alloy was employed as the diffusion source for grain boundary diffusion. The results show that Dy-Ce co-diffusion can effectively enhance the infiltration ability of diffusion source. The maximum coercivity increment of up to 795 kA/m can be achieved when x=10 due to the deeper diffusion depth and higher Dy content in the shell, while a significant degradation of remanence is also exhibited due to the formation of a larger number of Dy-rich grains. Thus, Ce content is regulated to inhibit the deterioration of remanence. Increasing Ce content to above x=30, it is found that the formed CeFe2 phase near the surface can regulate the infiltration ability of diffusion source, reducing the area fraction of Dy-rich grain region that is detrimental to the remanence, and eventually, when x=50, the remanence is recovered to be comparable to that of as-prepared magnet, with a coercivity increment of 430 kA/m concurrently. This suggests that rationally designing the diffusion source composition enables the preparation of cost-effective magnets.