M sequence has good pseudo－random characteristics, but its linear complexity is not high and the nonlinearity is zero. So the application fields of m sequence are limited. Adopting the B－M algorithm this paper gives the studies of the linear complexity of m subsequences which are constructed. We get conclusion that the linear complexity of m sequence is bigger than m subsequences', approaching the half of the sequence's length. The nonlinearity of the m subsequence is analyzed using the Walsh spectrum technology. The simulation and the calculation results show that the nonlinearity of m subsequence has made a lot of improvement compared with the m sequence, and can be widely used in flow password, channel coding, spread spectrum communication, etc.