Lattice structures and thin-walled tubes are two types of energy-absorbers widely studied and applied in engineering practice. In this study, a new type of lattice-structure filled thin-walled tube (LFT) was proposed. In this new type of LFT, a BCC-Z lattice structure was filled into a square thin-walled tube. Then using data mining, a 3-D geometric design with five design variables was conducted on this new LFT. Using Latin Hypercubic sampling algorithm, 150 design cases were generated. Numerical models were then developed to simulate their crush behavior, and the simulation dataset was used for data mining. The results showed that (1) Filling the BBC-Z lattice structure into a thin-walled tube can significantly improve the energy absorption (EA) capacity of the structure. (2) The decision trees generated in the data mining process indicated that the rod diameter d of lattice structure is the key design variable that has most significant impact on EA, followed by m and n. (3) The design rules to build LFTs with high EA efficiency (SEA>=16 kJ/kg and CFE>=45%), high total EA (SEA>=16 kJ/kg and EA>=6 kJ), and lightweight (SEA>=16 kJ/kg and Mass<=0.45 kg) were obtained from decision trees. The ideal configurations of LFT corresponding to these three objectives are: d>2 mm, n>2 and m>3 for high EA efficiency; d>2 mm, n>2 and m>3 for high total EA; and d>2 mm, n>2, m<=4 and t<=1.7 mm for lightweight.