Abstract: Droughts frequently occur in karst areas because of the topographic features. In order to study the allocation of water resources under drought conditions in karst areas，a multi-objective optimization model of water resources allocation based on a genetic algorithm is proposed. Taking Nandan County in Guangxi Province as an example，a water resources optimal allocation scheme in Nandan County under drought conditions in 2020 was analyzed. Based on the results，countermeasures for water shortage were put forward. The results show that in 2020，under the normal water demand program，the water shortage in Nandan County is relatively large，but under the compressed water demand scheme，the demand for social and economical in the area of townships can be basically met. It is suggested to use the compressed water demand scheme in drought years，which provide theoretical and technical support for flood control and drought relief department.