The invention discloses a waste rubber powder modified asphalt composition and a preparation method thereof. The waste rubber powder modified asphalt composition comprises the following components in percentage by weight: 60-94 percent of basic asphalt and 6-20 percent of activated waste rubber powder. The preparation method comprises the following steps: adding the activated waste rubber powder into the melted basic asphalt for fully mixing to obtain the waste rubber powder modified asphalt composition. The asphalt composition disclosed by the invention is high in storage stability and low in cost, and the raw materials are easily available; the asphalt component has a wide application prospect in the fields of road engineering, waterproof coiled materials and the like.