Sample information-extracting with diffraction enhanced imaging (DEI) has been one of the interesting areas for many years. Using cosine curve to fit rocking curve in DEI, we deduce the equations described by cosine functions for peak-position image, low- and high-angle image. The analytical expressions of absorption image, refractive angle image and scattering image are also developed. Then a simple method is proposed for sample information-extracting with DEI based on those deductions. This method can extract the absorption information, refractive angle information and scattering information of a sample using only three images, i.e. one peak-position, one low-angle image and on high-angle image, resulting in simple experimental process and low radiation dose introduced to sample by imaging process. The experiments are carried out on a standard sample and a real biological sample. For comparison, experiments are also carried out on the same two samples using the common multiple-image radiography (MIR) method, in which at least seven images should be used to extract sample information. Experimental results show that our new method does extract sample information successfully, and the results from our new method are comparable to those from the MIR method.