A working method of a multi-slot card reader based on the standard CCID protocol comprises: powering up to perform initialization, and establishing a connection with a host through a USB interface; when a USB configuration instruction is received, returning configuration information of the USB interface to the host; waiting to receive an instruction delivered by the host, when a flag bit of a reset is detected, determining the type of the flag bit of the reset, for example, if the flag bit is a contact card flag bit, recording, according to the type of a change of a card placement pin level of a current contact card slot, a corresponding state of the contact card slot, or for example, if the flag bit is a periodic flag bit, sending a card search instruction corresponding to a current non-contact card slot, and recording a corresponding state of the non-contact card slot; and if the flag bit is a USB flag bit, performing a corresponding operation on a current card slot according to the received instruction. The card reader adopts a USB chip having multiple terminations and serves as a composite device of the standard CCID. When accepting access of a host, the card reader access different card slots through different terminations, so that the compatibility is desirable.