把它们放在 BEGIN 和 END 之间

Just put them between BEGIN and END

IF  EXISTS (SELECT ID, code FROM tblTabel WHERE ID = @ID and code = @Code) 
BEGIN
    UPDATE tblTabel SET ID = @ID,code = @Code WHERE ID = @ID
    UPDATE tblTabelB SET ID = @ID,code = @Code WHERE ID = @ID
    UPDATE tblTabelC SET ID = @ID,code = @Code WHERE ID = @ID    
END   
ELSE
BEGIN

INSERT INTO tblTabel (ID,code) VALUES ( @ID ,@Code);
END