In order to greatly improve the quality factor (Q) of a Nb superconducting cavity and reduce its power loss, we performed high-temperature nitrogen doping (N-doping) on the superconducting cavity, which is the most widely used method in the world. Based on the needs of large-scale accelerators at home and abroad, the Institute of High Energy Physics, Chinese Academy of Sciences, carried out researches on 1.3 GHz 1-cell superconducting cavities, including standard post-processing and N-doping. After data analysis and comparison, it can be found that the Q values of two 1.3 GHz 1-cell fine-grain superconducting cavities have been significantly improved. At the same time, the abnormal behavior of Q value depending on acceleration gradient (E_acc) was observed in low-temperature vertical test, which is called the "anti-Q-slope" phenomenon.