The present invention discloses a method for rapidly measuring the liquid phase diffusion coefficient based on liquid core column lens equal observation height. According to the present invention, the used liquid core column lens is used as the liquid phase diffusion cell and the imaging element; one height on a CMOS image acquisition system is used as the observation height, the relationship among the image width, the refractive index and the concentration is measured with two methods, the liquid phase diffusion coefficient is obtained through least square method fitting according to the concentration information reflected by the image, and the equal observation height method is verified by using the mutual diffusion system between 0.33 mol/L KCL solution and 3 mol/L KCL solution as the example; and the method has characteristics of rapid measurement (about 70min) and accurate measurement value (relative error is less than 2%), further improve the method for measuring the liquid phase diffusion coefficient by using the liquid core column lens, and proves that the system for measuring the liquid phase diffusion coefficient by using the liquid core column lens is stable, the calculation method is diverse, and the accuracy of measurement result is high.