Besides introducing some basic concepts such as fractal and fractal dimension, this paper describes several types of fractal dimensions. Based on geophysical characteristics of fractured formations of deep igneous rocks in Daqing, the paper tries to give an quantitative interpretation of fractures with the fractal theory in view of self similarity of fractures. According to the method described in the paper, the logging data from the fractured reservoirs in deep igneous rocks of Daqing were processed by programming, with the production introduced. Furthermore, the relationship between fractal dimension and fractures and the factors affecting the fractal dimension of fractures are discussed.