The invention relates to a compound boric acid barium cesium, a boric acid barium cesium nonlinear optical crystal, a preparation method and application. The compound has the chemical formula of CsBaB9O15 and the molecular weight of 607.54 and is synthesized through a solid phase reaction method. The boric acid barium cesium nonlinear optical crystal has the chemical formula of CsBaB9O15, the molecular weight of 607.54, the space group of -Cc-, the cell parameter a of 6.4918(4) , the cell parameter b of 11.4075(6) , the cell parameter c of 17.2571(9) , the cell parameter beta of 92.375(3), the cell parameter Z of 4 and the cell parameter V of 1276.88(12) <3>. The powder 1064 nm frequency-doubled effect of the compound is 2-3 times that of KDP; the 532 nm frequency-doubled effect is about 1 time that of KDP, the transmission region is 175 nm to 2600 nm, and the crystal grows through a flux growth method. The method is easy to operate and low in cost; the prepared crystal is free of deliquescence in the air, good in mechanical performance, not prone to breakage, stable in physiochemical property, easy to process and suitable for manufacturing ultraviolet/deep ultraviolet nonlinear optical devices.