Abstract: Through longitudinal mechanical property tests on different culm sections and node conditions of 3-5 year-old square bamboo samples from Zhaotong City, the test results were fitted using the normal, log-normal, and Weibull distributions. The results indicate that the mechanical properties along the grain of square bamboo follow a normal distribution. The node condition significantly affects compressive strength along the grain, with node-free culms exhibiting higher compressive strength than those with nodes. The average longitudinal compressive strength of bamboo culms without nodes, with nodes and diaphragms, and with nodes but without diaphragms were 64.53 MPa, 59.85 MPa, and 60.24 MPa, respectively. The average longitudinal shear strength of the bamboo culms was 32.59 MPa. The average compressive and tensile strengths along the grain of bamboo strips were 78.10 MPa and 168.65 MPa, respectively. Using a non-parametric method, the characteristic values of compressive and shear strengths along the grain of the culms were determined to be 62.62 MPa, 59.71 MPa, 61.77 MPa, and 31.38 MPa, respectively, while those of the bamboo strips were 75.78 MPa and 165.27 MPa, respectively. The target reliability is positively correlated with the resistance factor. For square bamboo materials with safety levels I, II, and III, the compressive resistance partial factors are proposed to be 1.52, 1.37, and 1.24, and the design strength values are 35.90, 39.83, and 44.00 MPa, respectively.