The invention belongs to the field of engineering risk evaluation, and particularly relates to an adjacent building safety quantitative evaluation method in tunnel construction. The adjacent building safety quantitative evaluation method in the tunnel construction mainly comprises the following steps of step 1, building an evaluation index system, step 2, building a standard extensible cloud model of evaluation indexes, step 3, computing and obtaining a weight matrix of the evaluation indexes through a subjective and objective weighting method, step 4, computing a relevancy matrix of a to-be-evaluated object through cloud relevancy computing, and obtaining a safety evaluation grade of the to-be-evaluated object through a weighted average method and combination of an evaluation index weighted value and the relevancy matrix, and step 5, measuring the reliability of safety evaluation grade. The adjacent building safety quantitative evaluation method in the tunnel construction combines advantages of a cloud model and an extensible theory, and provides effective decision support advices for protection and control of an adjacent building of different safety grades.