Top-seed infiltration and growth technique (TSIG) is proposed to fabricate Y-Ba-Cu-O (YBCO) single-grain superconductor nano-composites, in which a solid source composition of nano-Y2O3+BaCuO2 and a liquid source composition of Y2O3+10BaO+16CuO are employed. As can be seen, this novel technique uses just one source of precursor powder of BaCuO2, so it is more simplified and efficient. Microstructural observation indicates that fine Y2BaCuO5 (Y-211) inclusions with a size from dozens of nanometers to about one hundred nanometers are successfully introduced in YBa2Cu3O7-x (Y-123) superconducting matrix, which can act as more effective pinning centers for improving the bulk performance. Superconducting property measurement shows that, a maximum trapped field of 0.36044 T is present at the center of the sample after magnetization by a permanent magnet (B=0.5 T). These results prove that our proposed TSIG technique is a practical method for fabricating YBCO bulk superconductor nano-composites with high performance.