Thanks to the strong perpendicular magnetic anisotropy (PMA), excellent processing compatibility as well as novel spintronic phenomenon, Co/Pt multilayers have been attracting massive attention and widely used in magnetic storage. However, reversed magnetic domains come into being with the increasing layer repetition ‘N’ to reduce magneto-static energy, resulting in the remarkable diminishment of the remanent magnetization (M r). As a result, the product of M r and thickness (i.e., the remanent moment-thickness product, M r t), a key parameter in magnetic recording for reliable data storing and reading, also decreases dramatically. To overcome this issue, we deposit an ultra-thick granular [Co/Pt]80 multilayer with a total thickness of 68 nm on granular SiN x buffer layer. The M r t value, M r to saturation magnetization (M s) ratio as well as out of plane (OOP) coercivity (H coop) are high up to 2.97 memu/cm2, 67%, and 1940 Oe (1 Oe = 79.5775 A⋅m−1), respectively, which is remarkably improved compared with that of continuous [Co/Pt]80 multilayers. That is because large amounts of grain boundaries in the granular multilayers can efficiently impede the propagation and expansion of reversed magnetic domains, which is verified by experimental investigations and micromagnetic simulation results. The simulation results also indicate that the value of M r t, M r/M s ratio, and H coop can be further improved through optimizing the granule size, which can be experimentally realized by manipulating the process parameter of SiN x buffer layer. This work provides an alternative solution for achieving high M r t value in ultra-thick Co/Pt multilayers, which is of unneglectable potential in applications of high-density magnetic recording.