The invention relates to a method and device for measuring regular expression state complexity. The method for the measuring regular expression state complexity comprises the steps that firstly, the curly relationship between any two states p and q in a given non-deterministic type finite automation M is judged, and the curly relationship is one of the five kinds of relationships: the mutual-exclusion relationship, the equivalence relationship, the included relationship, the including relationship and the independent relationship, M = (Q, sigma, delta, q0, F), the Q is a finite set, each element of the Q is called as a state, the sigma is a finite alphabet, each element of the sigma is called as an input character, the delta is a state transition function, and the q0 belongs to the Q, the q0 is the unique starting state, and the F is a terminal state set; two, the regular expression state complexity is estimated according to the judging result of the step one, the state complexity is the state number/Q'/of the deterministic type finite automation M'obtained by determining the M, and the M'=( Q', sigma, delta', q0', F'). The method and device for measuring regular expression state complexity can obtain the reasonable estimating value rapidly, and improve measuring efficiency.