excel中IF函数请教?请高手帮帮忙，谢谢！

你写的公式在格式上有错误 如 00,A1<50)
因此公式可以写成
=IF(A1=0,"未用",IF(AND(A1>0,A1<50),"低",IF(AND(A1>=50,A1<100),"中",IF(AND(A1>=100,A1<200),"高",IF(AND(A1>=200,A1<500),"正常",IF(A1>=500,"优"))))))

公式只要写成如下就行了
=IF(A1=0,"未用",IF(A1<50,"低",IF(A1<100,"中",IF(A1<200,"高",IF(A1<500,"正常","优")))))
或者改写成
=IF(A1="","",LOOKUP(A1,{0,"未用";0.00001,"低";50,"中";100,"高";200,"正常";500,"优"}))

=IF(A1="","",LOOKUP(A1,{0,"未用";0.00000008,"低";50,"中";100,"高";200,"正常";500,"优"}))

=if(a1<=0,"未用",if(a1<50,"低",if(a1<100,"中",if(a1<200,"高",if(a1<500,"正常","优")))))

=Lookup(A1,{0,0.001,50,100,200,500},{"未用","低","中","高","正常","优"})

=LOOKUP(A1,{0,0.001,50,100,200,500},{"未用","低","中","高","正常","优"})