An illuminating building block with high light transmission having a positioning structure for a sheet-shaped electric connection member, comprising: a base including at least two recesses defined therethrough; a top cover being hollow and light transmittable, mounted on the base, including a top portion, a side portion and a bottom opening, the top portion including at least two hollow studs corresponding to the recesses of the base, the side portion extended from an edge of the top portion in a direction toward the base and connected with an edge of the base, the side portion including a plurality of projection strips disposed on at least one interior surface of the side portion, the projection strips projected from the interior surface of the side portion toward an interior of the top cover and arranged at intervals, a plurality of slots provided between the projection strips and disposed spaced away from each other, the bottom opening being surrounded by the side portion; a circuit board disposed on a top of the base, the circuit board including at least one electrode circuit disposed at a side facing the base and corresponding to positions of the recesses, the electrode circuit being electrically connected with at least one electric connection member that is extended in a direction towards the top portion, wherein the electric connection member has a sheet-shaped structure, the electric connection member includes a projection portion, at least two elastic pieces and a connection portion, the projection portion has two ends, one end of the projection portion is electrically connected with the electrode circuit and another end of the projection portion is connected with the connection portion, the projection portion of the electric connection member is inserted into the slot, the elastic pieces are projected out of the hollow studs, and the connection portion connects the projection portion with the elastic pieces; and at least one illuminating member mounted on the circuit board. a base including at least two recesses defined therethrough; a top cover being hollow and light transmittable, mounted on the base, including a top portion, a side portion and a bottom opening, the top portion including at least two hollow studs corresponding to the recesses of the base, the side portion extended from an edge of the top portion in a direction toward the base and connected with an edge of the base, the side portion including a plurality of projection strips disposed on at least one interior surface of the side portion, the projection strips projected from the interior surface of the side portion toward an interior of the top cover and arranged at intervals, a plurality of slots provided between the projection strips and disposed spaced away from each other, the bottom opening being surrounded by the side portion; a circuit board disposed on a top of the base, the circuit board including at least one electrode circuit disposed at a side facing the base and corresponding to positions of the recesses, the electrode circuit being electrically connected with at least one electric connection member that is extended in a direction towards the top portion, wherein the electric connection member has a sheet-shaped structure, the electric connection member includes a projection portion, at least two elastic pieces and a connection portion, the projection portion has two ends, one end of the projection portion is electrically connected with the electrode circuit and another end of the projection portion is connected with the connection portion, the projection portion of the electric connection member is inserted into the slot, the elastic pieces are projected out of the hollow studs, and the connection portion connects the projection portion with the elastic pieces; and at least one illuminating member mounted on the circuit board.