A method and device for preparing karst caves based on 3D printing technology. The method includes the following steps: determining size of a sample according to test requirements, constructing a 3D karst cave digital model based on three-dimensional karst cave scanning result, and carrying out 3D printing by using alloy to form primary karst cave sample; preparing rock similar material mixture according to proportioning scheme; pouring mixture into sample mold while burying karst cave model into mixture according to position of a karst cave; curing sample together with mold at room temperature until rock similar materials get hardened, removing mold, curing formed karst cave rock sample at constant temperature and constant humidity and then baking or heating same by electrifying heating wire in alloy to form rock sample with hollow karst cave; and filling hollow karst cave with different fillings to form different type of karst cave sample.