<%
strO="abcdefg<pre>h001</pre>abcdefg<pre>h002</pre>abcdefg<pre>h003</pre>abcdefg<pre>h004</pre>3"

response.write strO & "<br>"

strNew=f_replace_middle(strO,"<pre>","</pre>","OK")

response.write strNew

function f_replace_middle(strO,strA,strB,strN)
    '替换strA和strB中间的字符串成新字符串
    lengthA=len(strA)
    lengthB=len(strB)
    lengthN=len(strN)

    insA=instr(strO,strA)

    do while insA>0
        insB=instr(insA+lengthA,strO,strB)

        if insB>0 then
            strO=left(strO,insA-1) & strN & mid(strO,insB+lengthB) '变成新字符串
            insA=instr(strO,strA)'对于新字符串指针必须重新来
        else
            exit do
        end if
    loop
    f_replace_middle=strO
end function
%>

运行结果是：

abcdefg
h001
abcdefg
h002
abcdefg
h003
abcdefg
h004
3
abcdefgOKabcdefgOKabcdefgOKabcdefgOK3