Microcode combination of complex instructions is shown. A microprocessor includes an instruction queue, an instruction decoder, and a microcode controller. The instruction decoder is coupled to the instruction queue. The microcode controller is coupled to the instruction decoder and has a memory. The memory stores a combined microcode for M complex instructions arranged in a specific order, where M is an integer greater than 1. When the M complex instructions in the specific order have popped out of the first to M-th entries of the instruction queue, the instruction decoder operates the microcode controller to read the memory for the combined microcode with microcode reading trapping happened just once.