The Jiangmen Underground Neutrino Observatory (JUNO) is building a 20-kt liquid scintillator detector in a laboratory 700~m underground to address many important topics in neutrino and astro-particle physics. A clean and low radon environment is quite important to build an ultra-pure detector with the lowest radioactive background. In this work, we present the main strategies of radon and cleanliness control at JUNO. The total volume of the experimental hall is about 120,000 m$^3$. We have implemented clean room management in the laboratory, and the final cleanliness can be equivalent to class 10,000-100,000 level. There is a large amount of underground water at the JUNO site, and the flow rate can reach 450 m$^3$/h with 120,000 Bq/m$^3$ radon concentration in the water. We have validated that the underground water is a big radon source for radon in underground air. The nominal radon concentration in the main hall is required to be below 200 Bq/m$^3$ for human beings' health and neutrino physics, and the maximum value should be below 400 Bq/m$^3$. With great efforts on optimization of the ventilation underground and well isolation of the experimental hall, the final radon concentration in the main hall has reached 100-200 Bq/m$^3$.