Single domain YBCO bulk superconductors are fabricated by the top-seeded infiltration and growth process(TSIG). The effects of different particle size Y2Ba4CuBiOy nanoparticles doped on the growth morphology, microstructure and levitation force of single domain YBCO bulk superconductors are investigated. The mean diameters of the initial Y2Ba4CuBiOy nanoparticles respectively are 283 nm, 170.4 nm and 82.5 nm, and the amount of Y2Ba4CuBiOyadded to Y2BaCuO5 is 2 wt%. The results show that the single domain YBCO bulk superconductors can be fabricated, and the surface of the sample has significant cross pattern and four single domain sectors become smooth and flat. The second phase Y2Ba4CuBiOy nanoparticles are well-distributed into the single domain YBCO bulk samples, and the particles sizes of Y2Ba4CuBiOy nanoparticles in the YBCO bulk sample are respectively 270 nm, 150 nm and 50 nm, smaller than that the initial powder. The magnetic levitation forces of the samples increase gradually with the decrease of initial powders of Y2Ba4CuBiOy nanoparticles, which are respectively 10 N, 17 N and 22 N. The results are very important for further studying the method of flux pinning of nanoparticles and improving the properties of YBCO bulk superconductors.