Dear @Yingxin.Lv,
Yes, you can calculate the tower-base loads (and other loads) from the states after solving the equations of motion, but the calculation is not straightforward. To calculate the tower-base loads, ElastoDyn uses a load-summation procedure as summarized in the following forum topic: Tower Base loads. The details are explained in the ElastoDyn theory documentation on readthedocs, specifically the FASTLoads.doc document: 4.9. ElastoDyn Users Guide and Theory Manual — OpenFAST v4.1.2 documentation.
This is in contrast to a displacement-based approach, e.g., as discussed in the following forum topic: Root moment of blades verification from mode shape function.
Best regards,