Abstract: With the continuous development of urban underground space, the number of underground structures and structures such as subways, underground shopping malls and underground passageways increases sharply, and the number of new road subgrade projects that span the existing underground structures and structures is increasing day by day. A new road subgrade crossing the existing shallow buried reinforced concrete rectangular tunnel in lacustrine soft soil area of Dianchi Plateau in Kunming is taken as the research background, the safety impact of new road engineering crossing the existing shallow buried reinforced concrete rectangular tunnel is analyzed, an evaluation method based on theoretical calculation is proposed, the internal force and displacement of the existing tunnel structure caused by road construction and operation are analyzed, and the evaluation criteria of whether the influence on the safety of the existing tunnel structure is given, can provide higher reference value for similar engineering projects.