Regarding the large storage space occupied by the encoding and decoding data of spatiotemporal grid voxels, we propose a low computational method to store the encoding and decoding of spatiotemporal voxels based on hexadecimal tree index structure, and establish a mathematical model of encoding and decoding to realize the identification and location index of voxels. We employ the automatic encoding and decoding method of 3DGIS to achieve the conversion of encoding and decoding storage representation of spatiotemporal voxels. Secondly, using the Galois finite field theory, we build a binary encoding and decoding matrix of grid voxels as well as a low computational optimization algorithm to realize calculation optimization in the storage process of voxel encoding and decoding. Finally, taking the deposit block data of a mine as an example, the grid voxel codec model, storage representation conversion and low computational optimization algorithm are put into practical application. The proposal is compared with the Morton code of the octree index structure.  The results show that the proposal can effectively reduce computational cost of encoding and decoding storage by about 30%, as well as the spatiotemporal efficiency for storing grid voxels.