A safety cover used in a sand grinder is disclosed to include a cover body rotatably mounted at the base of the sand grinder around the sand wheel and having equiangularly spaced oval locating holes, a positioning device selectively engaged into one of the oval locating holes, and a switching lever mounted at the base and biasable between a locking position where an abutment portion of the switching lever is abutted against the positioning device to lock the positioning device in one oval locating hole and an unlocking position where a bearing portion of the switching lever faces toward the positioning device for enabling the positioning device to be disengaged from the respective oval locating hole.