The dimensional accuracy of investment castings is greatly affected by the linear shrinkage rate of the wax mold. Reducing the linear shrinkage rate of the wax mold is an effective measure to improve the dimensional accuracy of castings. The influence of a hollow wax mold on the dimensional accuracy of a K648 superalloy casting was studied. The results show that a hollow wax mold can alleviate the problems of plane shrinkage and local deformation of the investment mold. The average linear shrinkage of the wax mold is reduced from 1.16% to 0.54%, the dimensional accuracy of the casting can be improved from CT7 to CT5, and the shrinkage of the casting is reduced from 2.70% to 2.41%. The present research can provide a reference basis for improving the dimensional accuracy of thick and large investment castings.