A multifunctional portable data card and a data transmission method are provided. The data card includes a main control module, a gear selection module, a data transmission module, an interface module and a storage module. The main control module detects a gear selection signal generated by the gear selection module, and sends a corresponding operation command to the data transmission module according to a working mode corresponding to the gear selection signal; the data transmission module performs data transmission in the data transmission mode or the OTG data processing mode after receiving the operation command; the interface module provides a port for interaction between the multifunctional portable data card and an external device; and the data card further includes the storage module.