Abstract: The development of deep-UV nonlinear optical crystals in China is reviewed,with a focus on KBe₂BO₃F₂ (KBBF). Its discovery, crystal growth, prism-coupled device technology,and capability for producing deep-UV coherent emission are discussed. Finally, we describe the fruitful applications of deep-UV lasers based on KBBF in advanced scientific instruments such as ultrahigh resolution photoelectron spectrometers, and present an outlook of further potential application fields in the future.