In this paper, the micro-structural observation with scanning electron microscopy (SEM) and the angle-changed shear strength test of the Jurassic red-bed sandstone, siltstone and mudstone samples which were collected from Pingshan County in Sichuan Province and Suijiang County in Yunnan Province were conducted. The results show that the shear strength and porosity of the red-bed soft rock have a negative exponential relationship; the shear strength and particle roundness and particle orientation have a negative linear relationship; the shear strength and the Euler number have positively correlated linear relationship.