A compact continuous wave (CW) 589 nm laser is reported by intracavity sum-frequency mixing in a composite cavity. The laser has two sub-cavities. Nd:YAG crystal and Nd:YVO4 crystal were pumped by two laser diodes respectively in the two sub-cavities. In the two cavities wavelengths of 1319 nm from Nd:YAG (corresponding to the 4F3/2-4I13/2 transition) and 1064 nm from Nd:YVO4 (corresponding to the 4F3/2-4I11/2 transition) were chosen to be mixed into 589 nm laser. Through designing of the cavity, the optimum matching of modes and gains for the two wavelengths was obtained. In the overlapping of the cavities, sum-frequency mixing was generated with a type I critical phase matching BiB3O6 (BIBO) crystal. A stable laser output of 24 mW at 589 nm with low noise was obtained at the incident pump power of 750 mW for the Nd:YAG crystal and 600 mW for the Nd:YVO4 crystal.