Water-soluble Mn2+ doped CsPbCl3 nanocrystals coating by 6-aminocaproic acid (ACA) ligand were prepared by a simple ligand assisted reprecipitation method at room temperature. The CsPbCl3:Mn2+/ACA nanocrystals were almost cubic phase and had mean size of about 10 nm. Due to the coating and passivation of ACA, the CsPbCl3:Mn2+/ACA nanocrystals retained the initial fluorescence intensity of 20% after being dispersed in deionized water for 20 days. The orange LED device based on CsPbCl3:Mn2+/ACA nanocrystals were prepared with excellent luminescence properties. In the cytotoxicity test, even if the MCF-7 cells were cultured for 24 h at the concentration of CsPbCl3:Mn2+/ACA nanocrystals as high as 160 μg·ml−1, the cell survival rate was still 70%. Confocal fluorescent cell imaging results showed that the nanocrystals had remarkable fluorescent cell imaging effect even after 24 h. The synthesized CsPbCl3:Mn2+/ACA nanocrystals have nice water solubility, good water stability, low cytotoxicity and highly luminescence properties, and have great application potential in the field of orange LED and fluorescent probes.