Linear Cryptanalysis is one of the most important attacks on block ciphers.In this paper

the linear provable security for a class of unbalanced Feistel networks is investigated deeply.Using the structure of linear deviation

we prove that the upper bound of r-round(

r≥m

) linear hull probabilities are bounded by LP×LP and r-round(

r≥2m

) linear hull probabilities are bounded by 2(LP× LP×LP×LP) when the maximal linear hull probabilities of round function is LP and rounds keys are independent and uniformly random.