A single-side tower-type roller system based asynchronous rolling mill for rolling an ultra-thin composite strip and a hydraulic system therefor are provided. The mill includes a machine frame and reel assemblies. An upper roller system assembly and a lower roller system assembly are arranged in the machine frame. A down-pressing assembly is arranged on the machine frame and used to adjust a roll gap between the upper roller system assembly and the lower roller system assembly. A support roller balance assembly is arranged on the machine frame and used to support and balance the upper roller system assembly. The lower roller system assembly includes right and left working rollers. The right working roller is a plain roller. The left working roller is a patterned roller. A left-pressing assembly is arranged on the machine frame and used to adjust a roll gap between the right and left working rollers.