Cesium lead halide perovskite quantum dots (PQD) have potential for development in display backlights due to its high color purity, high luminous efficiency, wavelength tunability, and easily production. However, its poor stability is the biggest obstacle in practical application. In this study, we use post-treated by controlling the ratios between PQD and ligands (oleylamine and oleic acid are mixed in a volume ratio of 1:1) solution to improve quantum yield (QY). The result shows that the emission wavelength and QY of as-prepared CsPbBr<sub>3</sub> QDs is 514 nm and 84 %, respectively. It was found that the QY of QDs increases with increasing the concentrations of ligands. The relative QY of the post-treated PQDs can be increased from 84 to 212 %, which depends on the ligand concentrations. After aging for one month, the QY of the as-prepared PQD reduces from 84 to 73 %, while no obviously QY decay can be observed for post-treated samples. The results show that post treatment by adding a ligand can improve QY and stability of PQDs effectively.