Novel three-dimensional hierarchical α-calcium sulfate hemihydrate twin-flowers with a self-symmetrical structure (3D α-HH HTFs) are synthesized successfully assisted by trisodium citrate (TSC). The morphology of α-HH is closely dependent on TSC, and with increasing TSC concentration from 0 to 15 mM, the morphology gradually evolves from a long column to rod, hexagonal plate, twin-flower-like, and eventually microgranule. 3D α-HH HTFs are formed via heterogeneous nucleation coupled with Ostwald ripening. The 3D α-HH HTFs are further used as an immobilized water material to separate water from a surfactant-stabilized water-in-oil emulsion, and exhibit excellent separation performance with a separation efficiency of 99.31 wt % and immobilization efficiency of 93.03 wt %. Impressively, the separated solid after water separation can be regenerated into 3D α-HH HTFs, which retain the high separation performance of the original 3D α-HH HTFs. This work demonstrates that 3D α-HH HTFs are highly promising in purifying oil with undesired water contamination.