The study of rock micro-structure is very difficult at present. The micro-structure of the reservoir controls not only the micro-character of the reservoir but also the macro-character. Using the fractal theory and the data of mercury injection and thin-section from 3 wells about 40 samples in Shengtuo, the micro- pore structure characteristics of the reservoir was studied. Results indicate that the micro-structure shows fractal features to some extent. We measured the fractal dimension and built up the quantitative relation- ship of physical property and the micro-structure parameters with fractal dimension. We found they have good correlation and correlation of delta-front is better than delta-plain. Thus it can be seen that the fraetal dimension can reflect the complexity of the pore-space synthetically and it can be used to do comparative e- valuation for different reservoirs.