An automatic anti-pollution reverse osmosis unit includes an activated carbon fiber security filter, a high pressure pump, a single-section crossflow reverse osmosis membrane module, a circulating pump and an online protection liquid adding and dosing device, the connection order from a water inlet to an outlet through pipelines is as follows: the water inlet is successively connected with the activated carbon fiber security filter, the high pressure pump, the single-section reverse osmosis membrane module and the produced water outlet, wherein a concentrated water side of the single-section reverse osmosis membrane module is connected to the water inlet through the circulating pump, the single-section reverse osmosis membrane module is also provided with a concentrated water discharge outlet, the automatic anti-pollution reverse osmosis unit overcomes the design defects of conventional reverse osmosis systems, is suitable for engineering design of a sewage reuse system for water sources with high organic matter and microbe content, through the work of the security filter and linkage of the online protection liquid adding and dosing device with the open and stop of a reverse osmosis system, the whole reverse osmosis component is protected, the secondary breeding of microorganisms on the reverse osmosis membrane component is avoided, the protection provided by the invention is similar to the single membrane component storage and the component is full of a protection liquid, and the working life of the automatic anti-pollution reverse osmosis unit is improved.