Punch shear damage in unidirectional composites is an unique damage mode where mode II transverse fiber shear is the dominant micromechanical damage mode in addition to fiber-matrix interphase debonding, large deformation of matrix, and matrix cracking. A new punch shear experimental method has been developed to test unidirectional composite ribbons at sub-millimeter length scale. A 2D micromechanical finite element model has been developed and validated with the experimental data. The 2D micromechanical FEM model statistical mixed mode fiber fracture, and fiber-matrix debonding using zero thickness cohesive elements. Results show that an equivalent 2D micromechanical FE model can predict the micromechanical damage mechanisms under punch shear loading in addition to predicting the statistical stress-strain behavior similar to the experiments.