非常感谢，学习了，看了您的回复，一下子明白了，昨天纠结了一天，

do i=1        to dim(array);

    if array(i)=a then do;

        a_name=vname(x(i));
        leave;
end;

end;

谢谢楼上，vname函数学习了，太厉害了，顺便提一下其它函数，以便以后参考：
1.Functions That Determine SAS Variable Information ：
VTYPE,VTYPEX:To determine if a variable is character or numeric.
VLENGTH:        To return the storage length (determined at compile time) for a variable
VNAME:           To return the name of a SAS variable
VLABEL:           To return the label associated with a SAS variable
CALL VNEXT:    To determine the name, type, and length of one or more DATA step variables
VVALUE :         To obtain the formatted value of a variable

2.Functions That Determine Format Information 403
VFORMAT :     To return the format name associated with a variable
VFORMATD :   To return the format decimal value associated with a variable
VFORMATN :   To return the format name associated with a variable. The name includes the $ if the format is a character variable, but not the width of the decimal value.

VFORMATW :  To return the format width associated with a variable