Abstract: Through comparative analysis of function testing and trial of typical urban rail transit FAO (fully automatic operation) lines in Nanning, Suzhou and Shanghai, the practical problems in current work are analyzed elaborately. The interface of each work is sorted using critical incident method, as well as the logic relation between function testing and trial operation of FAO line. The differences between integrated joint commissioning and scenario verification are discussed. Through analogy method, the advantages and disadvantages of carrying out the work under different modes are expounded, and effective implementation suggestions targeting the existing problems in current urban rail transit industry are put forward.