Graph-ranking based methods have been developed for generic multi-document summarization in recent years and they make uniform use of the relationships between sentences to extract salient sentences. This paper proposes to integrate the relevance of the sentences to the specified topic into the graph-ranking based method for topic-focused multi-document summarization. The crossdocument relationships and the within-document relationships between sentences are differentiated and we apply the graph-ranking based method using each individual kind of sentence relationships and explore their relative importance for topic-focused multi-document summarization. Experimental results on DUC2003 and DUC2005 demonstrate the great importance of the cross-document relationships between sentences for topic-focused multi-document summarization. Even the approach based only on the cross-document sentence relationships can perform better than or at least as well as the approaches based on both kinds of sentence relationships.