Abstract: Pinus koraiensis, Larix gmelini and Larix olgensis are the species of the most important timber in northeast of China. The sample trees of the three softwoods for density and maximum crushing strength test are collected from the various sample plots through out the range of their natural distribution. Some of them had been collected and tested in the fifties, and some sample trees were complemented and tested late. The experimental results of wood are shown in this paper to study the variations in density and strength that may occur not only among the different localities but also among trees within a locality and within a tree.The variations in density and strength of each kind of wood are clearly shown in this research, and thus a reliable representative value (species mean and total variance of wood density and strength.) could be determinated respectively. In addition, the lumber stress grading and grade stresses or characteristic value are derived by different methods in this paper for the structural timber.