A transmission stopping device for a cordless curtain includes a box assembly and a stop wheel assembly disposed in the box assembly. The stop wheel assembly includes a torsion wheel and a stop wheel. The stop wheel is provided with balls therein. A rotation-stopping assembly is provided between the stop wheel and the box assembly. The cooperation between the balls of the stop wheel and the rotation-stopping assembly in the box assembly ensures that the ascent and descent of a curtain achieves an accurate positioning.