The invention discloses an automatic model making device. The automatic model making device comprises two rails, as well as an engraving machine and a mortar spraying and compacting device; the engraving machine and the mortar spraying and compacting device move back and forth along a length direction of the rails and can be positioned relative to the rails. The engraving machine comprises a plurality of engraving working units for modeling a terrain; an excavation elevation of each engraving working unit is independently set; the mortar spraying and compacting device comprises a plurality of mortar compacting working units which are used for carrying out cement sand rendering; a grinding elevation of each mortar spraying and compacting working unit is independently arranged. In the technical scheme, the automatic model making device is used for modeling the terrain of a model through the engraving machine and carrying out cement sand rendering to finish model making by utilizing the mortar spraying and compacting device. The error of terrain modeling between two sections of the model made by the automatic model making device is relatively small, even zero, and thus the accuracy of the finished product of a model test is improved. The automatic model making device is simple to operate, convenient to use and capable of being applicable to making of various physical models.