The invention belongs to the fields of microbial technology and biological control and particularly relates to bacillus amyloliquefaciens BA-KA4 and a screening method and application thereof. Bacteria are separated from soil, and an agar disk diffusion method is adopted for screening BA-KA4 out of the bacteria, wherein the inhibition ratio of BA-KA4 on cucumber botrytis cinerea is 65%, and BA-KA4 has stable inheritance. Through cultural characteristics, morphology and physiological and biochemical characteristics of the strain in combination with result reanalysis of a 16S rDNA sequence and a gyrB gene sequence, it is preliminarily identified that the strain BA-KA4 is bacillus amyloliquefaciens. The strain is stored with the accession number of CGMCC No.12190 in the Common Microorganism Center of China General Microbiological Culture Collection Center. The strain has the best control effect on the cucumber botrytis cinerea, a long lasting period and a broad antibacterial spectrum.