Concrete under uniaxial compression was scanned by industrial computer tomography(CT) in situ. By analyzing the CT images under different loads, the variations of mean gray value, gray value variance, porosity and fractal dimension with the increasing load were obtained. Combined with digital volumetric speckle photography(DVSP), the 3D displacement fields and strain fields were investigated. The results indicate that the development of the different size cracks in the specimen under different loads results in variations of the mean gray value, gray value variance, porosity and fractal dimension. Mean gray value and gray value variance indicate the whole development rule of micro cracks under CT resolution. Porosity and fractal dimension are better for the description of the cracks above CT resolution. The displacement fields and strain fields obtained by DVSP can visually reveal the development of strain localization areas caused by the micro cracks, which provides a new method to study the failure mechanism of concrete.