将Ｘ射线衍射峰位移法引入用于测量Ｆｅ－Ｍｎ－Ｓｉ合金的层错几率α．所需要的精确点阵常数由数值计算获得，并评价了内应力引起的峰位移对测量结果的影响．内应力引起的α测量值相对误差约４％，因而可忽略不计．研究结果表明，随Ｍｎ含量的减少或训练次数的增加，α增加．值得指出的是，峰位移法可用来测量单一的形变α，而不像峰位移法给出两种层错几率之和（α＋β），其中β是生长层错几率．鉴于所研究合金的形状记忆效应源于重叠的形变层错所生成的应力诱发马氏体，所以α的测量比（α＋β）更为重要． X-ray diffraction peak displacement method is introduced for measuring the stacking fault probability of Fe-Mn-Si alloy. The exact lattice constant required is obtained numerically and the effect of internal stress on the measurement results is evaluated. The relative error of the α measurement caused by the internal stress is about 4%, which is negligible. The results show that with the decrease of Mn content or training times, α increases. It is worth noting that the peak shift method can be used to measure a single deformation α, unlike the peak shift method which gives the sum of the two stacking fault probabilities (α + β), where β is the growth stacking fault probability. The α measurement is more important than (α + β) in view of the fact that the shape memory effect of the alloy under study is derived from stress-induced martensite formed by overlapping deformation faults.