may not be the best way, try this
*generate year
gen year=year(date(date,"YMD"))
sort id year
by id : gen y=_n
su y
local max=r(max)
gen var1 = .
replace var1 = 0 if y>1
forv i=`max'(-1)2 {
  local j1=`i'-1
  local j2=max(`i'-5,1)
  local jj=0
  forv j=`j1'(-1)`j2' {
    local jj=`jj'+1
    replace var1=var1+1/(year-year[_n-`jj']) if y==`i' & year-year[_n-`jj'] != 0
  }
}

谢谢回复，不明白最后一行命令为什么要加y==`i'？

the reason is that we want to sum over previous years' (up to 5) from this year (target), so using y==`i' for that reason.

不好意思，多问您的一个问题，命令里是怎么确保计算的是同一ID的出现次数的啊？似乎是以y为目标值的。

the for loop inside:

forv i=`max'(-1)2 {
...
}

will loop within the same id only because the data is sorted by id and we have y==`i' to make sure the sum is over the same id.