Abstract Toe weight is widely employed in the earth and rockfill dam reinforcement projects, but the theoretical analysis of its impact on the earth and rockfill dam is very vague and the sizes of the toe weight block are mostly determined empirically. In this paper, it researches and discusses the impact of weight block in front of the reservoir dam to the static and dynamic characteristics of earth and rockfill dam through combining the theoretical calculation with the numerical simulation analysis methods based on the specific engineering example. It shows that the length and height of the toe weight block together with the internal friction angle of the material greatly affect the stability of the dam. The length, height and the economic height ratio of the dam are obtained by optimization. The toe weight block length should be 0.45-0.55 times the length of the dam. The toe weight block height should be at least larger than 0.19 times the dam height. The larger is the height of toe weight block, the larger the safety coefficient is. But the toe weight block height should not be larger than 0.3 times the dam height. Placing weight block in front of the reservoir dam can effectively improve the initial stress of dam foundation, and enhance the capability to resist the liquefaction.