Abstract: Precision predicting is important for precision confirming of mechanical assembly. Considering the deviation sources and unified representation of dimension and geometric tolerance, the twist representation for geometric deviation is discussed. By analysis of geometric deviation accumulation between two mating or double mating surfaces, the deviation accumulation model called directed deviation graph (DDG) is proposed, and its construction process is introduced. Based on the DDG, the minimum path of weight for deviation accumulation and its generation by Dijkstra algorithm is put forward, and the linear assembly precision statistic and its calculation considering the minimum path is analyzed. By Denavit-hartenberg (D-H) method, the calculation process for spacial assembly precision statistic is further proposed. Considering the assembly precision statistic, the assembly precision evaluation and predicting based on multivariate statistic

Key words: Assembly deviation statistic, Assembly precision predicting, D-H method, Directed deviation graph, Minimum deviation path