Taking Chinese fir lumber as the research object， the dynamic elastic modulus range and the number of samples of mechanical stress graded lumber （MSGL） with different strength grades were compared， and the probability distribution and the reliability analysis for tensile strength parallel to grain of MSGL were explored. The results show that mechanical stress grading of Chinese fir lumber can be carried out based on dynamic elastic modulus. The number of samples of MSGL located in the main strength grade areas Q₂， Q₃ and Q₄ exceeds 90.0%， and the optimal probability distribution for tensile strength for MSGL is the lognormal distribution. The design value of tensile strength for MSGL is significantly higher than that of ungraded and visual graded lumber.