The invention discloses a novel multi-stage hydraulic cylinder. The novel multi-stage hydraulic cylinder is low in medium leakage rate and long in service life, and can work under a reliable and stable condition. A composite sealing system is used for sealing each column body and each column casing body of the multi-stage hydraulic cylinder, and consists of n-shaped sealing rings, channel holes and combined sealing elements. A sealing mechanism that the pressure of a working medium is dynamically self-balanced is adopted for the n-shaped sealing rings, so that the machining accuracy of the column bodies is not required to be improved after the n-shaped sealing rings are adopted, influence on the working conditions of the combined sealing elements in the composite sealing system is eliminated, and the multi-stage hydraulic cylinder has dual sealing effects achieved by the n-shaped sealing rings and the combined sealing elements. Compared with the conventional multi-stage hydraulic cylinder, the novel multi-stage hydraulic cylinder has the advantages and characteristics of low medium leakage rate, good sealing effects, long service life, reliability and stability in working and the like.