J=Jm1(λ1)⊕Jm2(λ2) is the Jordan normal form which has two Jordan blocks Jm1(λ1) and Jm2(λ2).J has square-rooting matrices iff one of following holds:
(i) λ1,λ2≠0;
(ii)λ1=0, but λ2≠0, then m1=1, or λ1≠0, but λ2=0, then m2=1;
(iii) λ1=λ2=0, then m1=m2,m1+1=m2 or m2+1=m1.And we give the expresses of square-rooting matices of J.