1. A method for activating an on-line patch, comprising: positioning an address of a patch function and an entry address of a to-be-patched function; writing, in a middle segment, a long-jump instruction for jumping to the patch function based on the address of the patch function and the entry address of the to-be-patched function, wherein the middle segment is a storage space, which is located before or after an entry position of the to-be-patched function and is capable of at least storing one long-jump instruction, and the entry address of the to-be-patched function represents the entry position of the to-be-patched function; and modifying an instruction at the entry position of the to-be-patched function to a short-jump instruction for jumping to the middle segment, so as to jump to the middle segment after the short-jump instruction is executed, and then to jump to and execute the patch function through that one or more instructions in the middle segment are executed, wherein the one or more instructions in the middle segment includes the long-jump instruction for jumping to the patch function.