As one of the most common defects induced by Automated Fiber Placement, in-plane fiber micro-buckling is characterized by a macroscopic value and its influence on composites tensile properties are studied in this article. The mathematical relationship between fiber microscopic distribution and geodesic curvature of non-geodesic fiber path is derived. Influences of in-plane fiber micro-buckling on tensile properties are analyzed by off-axis tensile theory and finite element analysis, and verified by experiments. Actual fiber microscopic distribution of in-plane fiber micro-buckling shows that it is reasonable to evaluate the scale of fiber micro-buckling by the geodesic curvature radius of curved fiber trajectory. Longitudinal tensile properties of lamina are dramatically influenced by in-plane fiber micro-buckling, while the influences of in-plane fiber micro-buckling on transversal tensile properties can be ignored. When A/L reaches 0.023, the longitudinal tensile modulus and strength of lamina decreased by 25.5% and 57.7%, respectively, compared with the lamina without any defects. Based on the conclusions made in this article, the scale of in-plane fiber micro-buckling can be predicted without metallographic observation. And the increase of structural efficiency and the loss of mechanical performance in consequence of non-geodesic fiber path could be evaluated for the optimization of fiber trajectory.