Abstract: This work presents the design and implementation of Memory Management Unit（MMU） in a 32-bit RISC microprocessor.Fix mapped address and address translation based on translation look aside buffer are supported.The design is done following a full custom flow，using SMIC 0.18 μm technology.The processor chip with this design inside is fabricated two times，and the test result shows that the MMU is function correct，and Linux operating system can boot up and run without any problem.