It is an important and urgent task to improve the luminous efficiency and emission bandwidth of existing luminescent materials with emission in near infrared (NIR) spectral region (especially for NIR-II spectral region from 1000 to 1700 nm). Herein, we report a novel Ni2+ doped phosphor Mg3Ga2GeO8: 0.8 %Ni2+ which exhibits ultra-broadband emission (from 1100 to 1700 nm, the full width at half maximum (FWHM) is up to 300 nm) with high quantum efficiency (The internal quantum efficiency (36.7 %) and external quantum efficiency (7.3 %) are relatively high in the reported Ni2+ dope NIR-II emitting phosphors). The phosphor presents desirable thermal stability of luminescence (At 373 K, it remains 56.2 % of the initial intensity at room temperature). This work not only provides an advanced NIR-II emitting phosphor which can be effectively pumped by commercial near ultraviolet light emitting diode chips, but also introduces a new strategy (that is to explore a suitable host in which there exists many different crystalline sites for the occupation of activators) for the exploration of efficient ultra-broadband NIR-II emitting phosphors.