A cell detecting system is herein disclosed, wherein a complex is formed with a first bioactive ligand coupling to a quantum dot and recognizing and coupling to a first receptor of a cell and a second bioactive ligand coupling to a magnetic bead and recognizing and coupling to a second receptor of the cell. The magnet is configured for attracting the complex. A quantum dot measuring system configured for measuring the fluorescence of the complex includes an excitation light source, an optical system, a detecting sensor and a data capturing unit, wherein the detecting sensor includes a photomultiplier tube measuring florescence of the quantum dot excited by the excitation light source. The present invention achieves the goal of specific cell detection with high sensitivity without performing cell incubation. A quantum dot measuring system is also herein disclosed.