We quantitatively investigated the effect of wavelength, core radius, and shell thickness on the photothermal properties of a single Au nanoshell using Mie theory, a size-dependent dielectric function, and heat equation to determine the maximum surface temperature change and optimal particle size under continuous laser excitation. First, the intensity and position of the resonance peak can be adjusted by changing the core radius and shell thickness of the Au nanoshell. The required particle surface temperature variation also can be obtained. Then, the maximum particle surface temperature change per unit incident light intensity γ_max at four typical wavelengths (800, 808, 820, and 1064 nm) in the near-infrared region and the corresponding optimal particle size is obtained to analyze the application of the photothermal properties of the particles. Finally, the particle size distribution with a particle surface temperature change per unit incident light intensity greater than 0.9γ_max at the above wavelength is given. This research is essential for photothermal therapy, plasmonic-assisted photocatalysis, and particle synthesis.