Abstract: The Beijing radioactive ion beam facility isotope separator on-line (BRISOL) is a radioactive ion beam facility based on a 100 MeV@200 μA proton cyclotron. The radioactive ion beams are produced by bombarding the thick target with proton beam provided by cyclotron. The mass resolving power of the BRISOL is better than 20 000. The first radioactive beams of 37K+ and 38K+ were generated at BRISOL with CaO targets in 2015, and the maximum current of the 38K+ beam is only 1×106 pps when the current of proton beam is 0.5 μA. The collinear laser spectroscopy experiments using 3743K+ beams will be carried out on BRISOL. The yields of 3743K+ would not be less than 1×106 pps in the experiment. In order to fulfill the requirements, it is necessary to increase the yield of radioactive ion beams. So a series of studies were carried out. The first step is the targets preparation. According to the requirements of the ISOL targets, CaO was selected as the targets material for the generation of radioactive ion beams. The CaO targets were prepared by cold pressing methods with Ca(OH)2, carboxymethyl cellulose (CMC) and deionized water. CMC was added as a binder and poreforming agent. Those materials were mixed in proportion and were cold pressed into desired shape. The thermal treatment was performed in a graphite furnace. After sintering, the targets were porous and then loaded into the targets container. The ion source with the ability of dual ionization mode, including surface ionization mode and FEBIAD ionization mode, was applied in the study. In order to improve the surface ionization efficiency for K, a 0.1 mm thick rhenium metal lining was installed on the inner wall of the cathode. Then an offline experiment was conducted and the spectra of CaO targets were measured. The experimental results show that Ca+ is ionized when the cathode current is high enough. Therefore, it is necessary to optimize the cathode currents for larger yield of K+. After that, an online experiment at BRISOL was carried out. The experiment results show that the 36.38,43,45.47K beams are produced successfully. The yield of 38K+ is increased to 1.12×1010 pps when the proton beam is 10 μA, the much larger yields are achieved through increasing proton intensities, optimizing both the structure of ion source and the targets working temperature. The development of CaO targets and the results of on-line experiment will be presented in this paper.