The invention discloses a method for detecting amount of diesel oil mixed in machine oil. The method comprises the following steps: configuring multiple groups of mixed oil samples according to a ratio Xi of different diesel oil contents in the machine oil; measuring the kinematic viscosity Vi of each group of mixed oil samples by utilizing a kinematic viscosity measuring apparatus; performing correlation analysis on two groups of data of the configuration ratio of the mixed oil samples and corresponding kinematic viscosities according to a statistical function CORREL to obtain a correlation equation Vi=KXi+N serving as basic data for saving according to a SLOPE function and an INTERCEPT function; measuring an actual kinematic viscosity value V of the mixed oil to be detected under the same temperature condition by utilizing the kinematic viscosity measuring apparatus when the mixed oil to be detected is specifically detected to obtain the diesel oil content ratio X in the machine oil in the mixed oil to be detected matched with the actual kinematic viscosity value V according to the correlation equation Vi=KXi+N. According to the method, the content of the mixed diesel oil in the machine oil can be detected by utilizing conventional equipment, the analysis method is simple and practical, and the investment cost is low.