I. Introduction
In 1911, Professor Heike Kamerlingh Onnes of Leiden cryogenic Laboratory of Leiden University in Netherlands found that mercury produced superconductivity at the temperature of liquid helium. Since then, many scholars all over the world have entered the field of superconductivity. Superconducting materials have different forms such as wire, tape, film, and bulk. Because of its flux-pinning characteristics, high temperature superconducting (HTS) bulk can stably suspend above the permanent magnet, so it has great advantages and potential in the field of maglev train.