Multiphoton fluorescence imaging, which uses near-infrared light excited multiphoton absorption process, has been widely applied in biological imaging, especially in in vivo deep-tissue imaging due to its deep penetration, high spatiotemporal resolution, high signal-to-noise ratio, and low phototoxicity. Compared with UV-vis light used in traditional one-photon bioimaging, near-infrared light greatly improved the penetration depth of multiphoton fluorescence imaging. Recently, the light in near infrared-II region (1000-1700 nm) has attracted tremendous attention in one-photon and multiphoton fluorescence imaging, which further improves the imaging depth due to its lower scattering and better penetration capability in biological tissues. In this review, we introduce the mechanism of multiphoton fluorescence imaging and the properties of near-infrared light in biological tissues. Furthermore, we introduce and discuss recent advances in near infrared-II light excited multiphoton fluorescence imaging. Finally, we present challenges facing this technique and future developments.