A firmware extension method is provided, particularly adaptable for an embedded system. Firstly, a baseline firmware image is provided with a header file. Secondly, an extension firmware image is generated based on the header file, comprising one or more extended functions. Thereafter, a callback table is generated, comprising pointers pointing to entries of the extended functions in the extension firmware image. Further, memory allocation parameters are provided. The memory allocation parameters comprise a base address where the extension firmware image starts. The baseline firmware image, the extension firmware image and the callback table are then merged to generate a merged firmware image based on the memory allocation parameters.