The martensite structure and order state of Cu-18Zn-14Al alloy was studied by means of X-ray diffraction. The alloy was subjected to four different quenching treatments. As the quenching rate decreased, the nnn order degree of the alloy increased and the nn order degree remained almost unchanged. The splitting parameter p = \sin(2)theta(1) - sin(2)theta(2)\ and the monoclinic angle beta changed very little. In addition, the order state of the alloy was calculated according to its crystal structure model. It is suggested that only the Zn and Al atoms exchange along the b-axis as the nnn order decreases, which slightly influences crystal symmetry and lattice constant. (C) 2005 Springer Science + Business Media, Inc.