there are more than twice as many employees in Department X

more than 是多于,超过.超出的意思
as many.as 和.一样多
twice as many employees in Department X as in Department Y 意思是 X部门员工是y 部门的两倍 再把more than 加上 就是 X部门的人员是Y部门人员的两倍 多