In this paper for a given normal block matrix GD = ( A B C D ) that A 2 Cnn;B 2 Cnm;C 2 Cmn;D 2 Cmm and RankfGDg < n + m1 and given eigenvalues of M= DCA1B as 1; 2; ; m, we nd a remarkable formula for distance set of matrix GD0(same to GD instead of D we set matrix X) to GD as (GD;GD0 ) = (jmj+jm1 j 2 )1 2 where GD0 is a normal matrix