SARS is a positive-stranded virus featuring the largest viral RNA genomes today. The viral main proteinase(Hydrolase), controlling the activities of SARS virus replication , is an attractive target for therapy. We determined crystal structure for transmissible gastroenteritis virus(TGEV) hydrolase, and constructed a homology model for SARS coronavirus proteinase on Silicon Graphics station by Insight Ⅱ molecule simulation software. The structure may reveal remarkable degree of conservation of the substrate binding sites. We design an imaginable peptide precursor for inhibitor, and the base shape of pocket and property of the residues may be used as a basis for designing anti-SARS drugs.