data AA;
infile "E:\aaaa.txt";
  input x1 $1-3 x2 @4 ;
run;

谢谢，不过我找到了一个可以点出来的：file->import data->use-defined forma->options->style of input->Column

有一个新问题，要是长度不一样怎么办？
我能不能把比如
4-8位的数组成一个整数，然后先判断这个整数是否复合某个条件，然后再决定是存1-3位还是存1-4位？

Sorry for cannot type Chinese on my computer.

Just give you a simple example and hope it helps.

data temp;
  input x $;
datalines;
1234567
23456789
;
run;

data temp1;
  set temp;
  substring_4_8 = substr(x, 4);
* you can use other conditions;
  if length(substring_4_8) = 5 then do
    x1 = substr(x, 1, 3);
    x2 = substr(x, 4);
  end;
  else do;
    x1 = substr(x, 1, 4);
    x2 = substr(x, 5);
  end;   
run;

受教受教！