A novel 3-D coordination polymer with trimeric copper (I) unit, [Cu3(CN)(IN)2]n (IN = isonicotinate), was hydrothermally synthesized by the reaction of Cu(NO3)2·3H2O with isonicotinic and terephthalic acids. The structure was characterized to be a twofold interpenetrated 3-D coordination network polymer with two-coordinated copper(I). It has a powder SHG efficiency about that of KDP.