By investigating the regulation of the Xigua-Mengsong shoal group in the Level IV waterway construction project on Lancang River，this paper discusses the problem that the construction over-excavation in shoal group reaches can cause an adverse effect on the regulation effect and produce new navigation-obstructing areas. It then combines field measurement data and a physical model to explore the navigation-obstructing characteristics of shoals and the water surface，flow velocity，and parameters of rapids abating before and after regulation. The results indicate that regarding the construction in complex reaches with dense shoals，over-excavation leads to a shoal regulation effect falling short of the design expectations and even creates new navigation-obstructing areas. Appropriate remedial measures，such as backwater and flow diversion，can achieve the expected regulation effect. Future construction at similar shoals should strictly control over-excavation to ensure the regulation effect.