The invention is suitable for the technical field of storage, and provides a universal serial bus interface and a circuit thereof and a USB flash disk. The universal serial bus interface includes an interface unit, a first switch unit, a first main control chip, a second switch unit and a second main control chip, the interface unit can be connected with a computer or an adapter, a power supply output end of the interface unit is connected with a power supply input end of the first switch unit and a power supply input end of the second switch unit, the output end of the first switch unit is connected with a power supply pin of the first main control chip, a control pin of the first main control chip is connected with a controlled end of the second switch unit, and the output end of the second switch unit is connected with a power supply pin of the second main control chip. Connecting objects of the universal serial bus interface are distinguished through hardware, according to the different connecting objects, the different main control chips are started, it is unnecessary to use a single-chip computer, the connecting objects of the universal serial bus interface can be distinguished simply through a simple circuit structure, and the universal serial bus interface has the advantages of being low in cost and high in efficiency.