This paper presents an Artificial Immune Algorithm (AIA)simulating the biological immune systems, andoffers its basic principle and approach. Comparing AIA with Genetic Algorithm (GAs)simulating the biological evolu-tion process, the paper points out that the method producing new antibodies in AIA is more versatile than the oneproducing new individuals in GAs. AIA reflects mechanism of natural selection better than GAs does, as AIA selectseffective antibodies from all antibodies by the appetency between an antibody and an antigen and by the repulsion be-tween an antibody and another, while GAs selects new individuals of next colony by the proportion of individual fit-ness. For Travel Salesman Problem (TSP), this paper brings forward how to describe antibodies artificially, how toproduce original antibodies, how to compute the appetency between an antibody and an antigen and the repulsion be-tween an antibody and another, and works out several artificial immune operators producing new antibod-ies. Simulating examples show that AIA is a very effective method for TSP.