clear
input num
200306
200309
200312
200403
200406
200409
end

todate(num), gen(ym) p(yyyymm) f(%tmMonCCYY)      //you first have to find and install "todate"
gen yq=qofd(dofm(ym))
format yq %tq

我的为题已经解决，仍然非常感谢！一点分数不够意思~~

hplcdadong老师，这里请教下，您给的例子num本身是季度数据，那么
todate(num), gen(ym) p(yyyymm) f(%tmMonCCYY)
这句命令中p(yyyymm)为什么不能写为yyyyqq的形式？

还有，您的f(%tmMonCCYY)这个写法也没有看懂。   
谢谢

According to the original post, 200306, 200309 ... are actually year-month data. That's why I have to use p(yyyymm).  Then I converted it to year-quarter data using function "qofd".

If you type "help dates" in Stata, you'll find you can format year-month data in several ways, %tmMonCCYY is one way. You can simply use %tm.

I get it. Thanks very much for your kindly help.