Abstract: The first part of this paper gives complete collision rules for FHPⅡ 7-bits model of lattice gas automata. Some of them are irreversibe, them are different from the extension given by other authors.The second part is an example computed by the LGS method. Initial and boundary conditions are treated appropriately A random method is to ensure the conservation of the total particles number with a little stochastic fluctuation. Macro-velocitis are got through averaging over a time interval and smoothing on space. The results are in good agree ment with the classical concepts.