The invention provides an air quantity measuring method and an air quantity measuring device. The method comprises the following steps of: acquiring judgment parameters of n judgment factors input by a user; bringing the judgment parameters into 3 preset membership functions ri1, ri2 and ri3 of the corresponding judgment factors respectively to obtain a judgment parameter judging set Ri=(ri1, ri2, ri3) of each judgment factor, wherein the 3 preset membership functions of the judgment factors express small, moderate and big memberships of the corresponding judgment parameters respectively, and the membership functions are semi-trapezoidal functions; acquiring all judgment parameter judging sets, and forming a judgment matrix by using the membership of each factor judgment set as a row; calculating B=AoR, and obtaining an evaluation fuzzy set B=(b1, b2, b3), wherein A is the weight set A={a1, a2, a3, ..., and an} of the preset n judgment factors, and the weight set A should endow a corresponding weight ai=(i=1,2, ..., and n) for each judgment factor; and comparing a maximum element in the evaluation fuzzy set B=(b1, b2, b3), and acquiring the state expressed by the preset membership function corresponding to the element.