data test1 test2;
        set yourdata;
        seq=_n_; output test1;
        if a=1 then output test2;
run;

proc sql;
        create table want as
        select a.* from test1 as a, test2 as b
        where -40<=a.seq-b.seq<0;
quit;

嗯，非常感谢哈！很好！