Baseline is the basis and precondition of environmental damage identification and assessment. As one of the most widely used methods for baseline determination, the reference-site approach makes up for the shortage of historical data. However, as the key point of the reference-site approach, the selection of the reference site still has some problems, including the lack of clear standards and low credibility. To address these problems and provide a clear way and standard for the selection of reference sites, the reference site similarity evaluation index system for the soil baseline was proposed. Using the Shengli no.1 open-pit mine in Xilin Hot as an example, the baseline for soil damage was determined, and the result was compared with historical data. The results showed that the soil baseline calculated by the reference-site approach, to some degree, was authentic and reliable, and the practicability of the reference-site approach could be improved under the premise of ensuring the reliability of reference-site selection through controlling the main environmental factors related to the research.