Abstract At present, the MD5 algorithm in network security of got to a wide range of applications in many respects, but in be used actually face being hit by a "rainbow table" library of security risks, this design adopts the method of "salt", based on the proposed encryption definitely added to the random Numbers to reduce the risk. This article first introduces the principle and the risk for the MD5 algorithm and puts forward the theoretical basis to solve the problem, and then describes the improvement to solve the problem of the MD5 algorithm in FPGA to realize the overall architecture, analyses the function of each module, finally gives the Altera corporation based on series of the Cyclone II device DE2 system board the implementation of the results. Through the experimental results can be seen that the MD5 algorithm based on FPGA implementation has high processing speed and less resource usage, and based on FPGA and "salt" of plaintext processing can effectively reduce the use of the risk of "rainbow table" bump library, has certain practical value 1