Based on the finite element method, the seepage field of reinforced dykes of a reservoir is analyzed from hydro geological nature and characteristics of the impermeable wall. According to the typical cross-section of the reinforced dyke, performance-parameters of the dyke such as total water head, seepage velocity, seepage gradient are compared with the counterparts of the original dyke. Results in steady seepage are obtained. Generally seepage quantity decreases 45% from the original dyke. Permeability coefficients and defects of the impermeable wall are the most factors of affecting effectiveness of dyke reinforcement. Because piezometric tubes work well, measured dada are reliable, both measured and calculated data also coincide with each other well. The results show that the impervious reinforcing plan of the dyke is fit, the reinforced dyke can reach predeterminate impervious effects and meet the technical specifications. Safety of the reservoir is guaranteed.