The invention discloses a large dome magnetic building block which comprises a base and an upper cover fixed to the base. The upper cover comprises a square upper frame and a semicircular dome arranged on the upper frame, at least one magnetic block is arranged on the portion, corresponding to each side edge of the upper frame and a lower frame, between the upper frame and the lower frame, each pair of lower block ribs and one pair of corresponding upper block ribs cooperate with one corresponding outer convex rib, one corresponding inner convex rib and one corresponding frame rib to form a side wall of a containing groove for containing one corresponding magnetic block, an upper support rib strip is arranged in the upper frame, a lower support rib strip corresponding to the upper support rib strip is arranged in the lower frame, and the upper support rib strip and the lower support rib strip are both arranged in a cross mode. According to the large dome magnetic building block, at least one magnetic block is arranged on the portion, corresponding to each side edge of the upper frame and the lower frame, between the upper frame and the lower frame, so that it is guaranteed that the magnetic blocks can form attraction with other magnetic sheets serving as house walls; in addition, good positioning on the magnetic blocks can be achieved, and it is guaranteed that the magnetic blocks are stably and reliably installed and are not prone to fall off.