The invention discloses a hydraulic system of a lifting platform and belongs to the technical field of hydraulics. The hydraulic system comprises a reversing module, a speed adjusting module and a plurality of oil cylinder modules, wherein the reversing module comprises a proportional pilot valve and a hydraulic control reversing valve; an oil opening a of the proportional pilot valve is connectedwith an auxiliary pump of the hydraulic system; an oil opening c of the proportional pilot valve is connected with a first control oil opening of the hydraulic control reversing valve; an oil openingd of the proportional pilot valve is connected with a second control oil opening of the hydraulic control reversing valve; an oil opening a of the hydraulic control reversing valve is connected witha main pump of the hydraulic system; each oil cylinder module comprises a lifting oil cylinder; an oil opening c of the hydraulic control reversing valve is respectively connected with a rodless cavity of each lifting oil cylinder; the speed adjusting module comprises a plurality of speed adjusting valves; valve core openings of the speed adjusting valves are same; an oil opening d of the hydraulic control reversing valve is respectively connected with an oil opening a of each speed adjusting valve; and an oil opening b of each speed adjusting valve is respectively connected with a rod cavityof the corresponding lifting oil cylinder. The hydraulic system is capable of improving the lifting stability of the lifting platform.