sum是求几个变量的和，不是求一列的总和

你是每个文件里面就一个数据？一个文件里面的数据和减去另外一个文件里面的数据和？
如果是，你把两个文件导入就可以做了

data a;
infile "d:\data_*.txt";
input x;
run;

data a;
set a end=lastobs;
sum_x+x;
if lastobs;
run;

data b;
infile "d:\data_*.txt";
input y;
run;

data b;
set b end=lastobs;
sum_y+y;
if lastobs;
run;

data c(keep=sum);
merge a b;
sum=sum_x-sum_y;
run;