The invention provides a measuring method of solvent concentration in thickened oil. The measurement method of the solvent concentration in the thickened oil comprises the following steps of preparing solvent-thickened oil mixtures with different concentrations; measuring viscosities of the mixtures with different concentrations at the same temperature, and carrying out regression analysis to obtain a fitting viscosity function relation; measuring the viscosity of an oil sample acquired on site at the constant temperature to obtain the solvent concentration. The measurement method of the solvent concentration in the thickened oil provided by the invention is less in investment, low in workload, short in time, and more economical and feasible compared with a conventional complex separation process.