In order to obtain LD-pumped intracavity sum-frequency 491 nm blue laser, the oscillation conditions for the simultaneous dual-wavelength operation of 1063 nm and 912 nm were analyzed based on the threshold expressions of quasi-three-level and four-level system. In the experiment, a Nd∶GdVO4 laser crystal with doped concentration of 0.15% (atomic fraction) and size of 3 mm×3 mm×2 mm was pumped by a laser diode with the maximum output power of 3 W. A linear cavity setup was used to realize 912 nm and 1063 nm dual-wavelength operation. 0.8 mW 491 nm blue laser is obtained after a LBO crystal was inserted into the cavity as the sum frequency crystal.