A series of deep red phosphors with perovskite-like oxide LaSrGaO4 as host are synthesized by a high temperature solid state method, and the luminescence properties and mechanisms have been investigated in detail. LaSrGaO4 presents self-luminescence at 722 nm, and it is proved that the self-luminescence comes from two kinds of electronic defects and three kinds of vacancy defects, which are anti-occupation defects La-Sr(center dot), strontium gap defects Sr-i(center dot center dot), the oxygen interstitial defects O-i '', substitution defects Sr'(La), and strontium vacancy defects V-Sr ''. In addition, when Mn2+ ions are doped in LaSrGaO4 interestingly, the shape of the emission spectra of LaSrGaO4:Mn2+ is the same as that of LaSrGaO4, and the emission intensities are enhanced greatly. Luminescence of Mn2+ ions has been confirmed by doping Mg2+ into LaSrGaO4 and measuring the lifetimes of host LaSrGaO4, LaSrGaO4:Mg2+, and LaSrGaO4:Mn2+ for comparison. The mechanisms of host self-luminescence and Mn2+ luminescence are discussed by detecting the luminescence centers with the low temperature spectra, calculating the forbidden bandwidth with the diffuse reflectance spectra, and calculating the trap depths with the thermoluminescence spectra and further depicted by establishing the transition model. LaSrGaO4:Mn2+ can emit strong deep red light about 722 nm, so the phosphor will have a good application prospect in the field of plant lighting.