The invention discloses an Ethernet-based FPGA function online upgrading method. The method is applied to the function upgrading of a board card taking an FPGA as a main chip and having an Ethernet interface. A whole functional system comprises an upper computer part and a lower computer part, wherein the upper computer is mainly used for programming file reading, fragmentation, Ethernet packet assembling and sending; and the lower computer is mainly used for flash erasure and reading/writing, Ethernet packet analysis and feedback of an upgrading progress to the upper computer. By use of the method, the FPGA board card can be directly subjected to remote online upgrading through an Ethernet interface, so that unnecessary troubles and risk due to apparatus dismounting are avoided, the convenience and maintainability of device upgrading are improved, and the upgrading cost is reduced.