Abstract: In the research of slope engineering safety assessment, most of the researches focus on new slope and failure slope, but few on existing buildings slope (operational slope), and the assessment method is still lacking. Therefore, according to the fuzzy reasoning method, we propose a method of safety assessment for existing building slope based on fuzzy Petri net. The method adopts the credibility and change confidence of safety evaluation factors of the existing building slope, and uses the subjective and objective comprehensive evaluation methods to give the weight. The method can not only get the final results on the safety evaluation of the existing building slope, but also can calculate the first-level risk indexes that have the largest impact on the existing building slope safety, and the additional influence of variable factors on the safety and stability of existing building slopes. The method is used to the slope safety assessment of existing building slope behind a stamping plant, and the evaluation results is compared with the second-level comprehensive evaluation value of traditional fuzzy theory. The result shows that the presented method is feasible and the evaluation result is more reasonable. This research provides a new method for the identification and safety evaluation of existing building slope.