We propose a novel sandwich-structured electrochemiluminescence inununosensing platform using CdTe quantum dots (QDs)-embedded mesoporous silica nanospheres as enhanced signal probes for labeling the secondary antibodies and magnetite-silica-polystyrene (Fe3O4@SiO2@PS) nanocomposites as magnetic separable carriers for primary antibodies. The mSiO(2)/CdTe was successfully fabricated by loading CdTe QDs into mesoporous silica (mSiO(2)) and characterized by ultraviolet-visible spectra, photoluminescence spectra, transmission electron microscopy, fourier transform infrared spectrum and zeta potential. The electrochemiluminescence intensity of mSiO(2)/CdTe is much higher than that of CdTe QDs because a single mSiO(2) can encapsulate hundreds of QDs. Therefore, mSiO(2)/CdTe has been chosen as ECL labels for conjugation with secondary antibodies. Meanwhile, Fe3O4@SiO2@PS was used as a carrier of broad primary antibodies owing to convenient magnetic separation capability, large specific surface area, and the special force between the PS and antibodies. Carcinoembryonic antigen as a model tumor mark has been detected to prove the feasibility of our immunosensing platform. The immunosensor for carcinoembryonic antigen was successfully confirmed by cyclic voltammograms and electrochemical impedance spectroscopy. Under the optimal conditions, the immunosensor presented a linear range of 0.001 to 80 ng/mL for carcinoembryonic antigen detection with a low detection limit of 0.3 pg mL(-1) (S/N = 3). Furthermore, the immunosensor also displayed outstanding selectivity, good stability, and acceptable reproducibility, indicating its potential applications in clinical diagnostics.