Applications, such as high energy physics experiments at intensity frontier, time-of-flight positron emission tomography, ultrahigh repetition radiation imaging, and positron annihilation lifetime spectroscopy, etc., have raised increasing demands on the time response of scintillators. Development of ultrafast scintillators becomes one of focuses in recent studies. Barium fluoride (BaF2) crystal is a unique ultrafast scintillator with a sub-nanosecond fast scintillation component, its slow scintillation component with a decay time of about 0.6 μs, however, will cause serious pileups at high counting rates. As an effective approach to suppress the slow component in BaF2 crystals, doping has attracted continuous attention over the past three decades. This paper reviews the history of suppression of slow component in BaF2 crystals by doping, and then proposes basic principles on selecting doping elements. Suppression characteristic and mechanisms of slow component in BaF2 crystals doped with rare-earth metals (La, Y, Lu, Sc), alkali earth metals (Mg, Sr), transition metal (Cd), and alkali metal (K) are highlighted, and application research is introduced. The challenge and opportunity of slow component suppression by doping are also prospected.