Continuous-wave (CW) single-frequency coherent laser sources in the blue spectral region are useful for applications in biomedicine, metrology, display technology, atomic-trapping, quantum optics, and so on owingto their intrinsic merits of low-intensity noise, narrow linewidth as well as the good beam quality. The single-frequency 455 nm laser is in the band of blue-green (400～500 nm) optically transparent window of seawater, and seawater has very little photon absorption and low transmission loss. Moreover, the wavelength of 455 nm is just corresponding to the higher state excitation transition 6S127P32 of Cs atoms, which can be used for the development of long-distance underwater quantum communication based on quantum storage nodes of the cesium atom system. It also corresponds to the transition 6S126P32 of 138Ba2+, which can be used in the field of quantum computing to reduce systematic errors. In this paper, the continuous wave single-frequency 455 nm laser generation from intracavity frequency-doubled Ti:S laser is presented. By optimizing the curvature radii of the resonator mirrors, the beam waist of the fundamental wave at the Ti:S crystal is focused, and the threshold pump power is effectively decreased. When a quasi-phase matched MgO: PPSLT crystal is used as the intracavity frequency doubler, the highest output power of 427 mW at 455 nm is attained under the pump power of 11.5 W with an optical conversion efficiency of 3.7%. The measured blue laser beam quality is better than 1.18.