In this paper，a naked-eye magnetic molecularly imprinted photonic crystal sensor（MMIPCs） based on magnetic molecularly imprinted nanoparticles（MMINPs） for tetracycline（TC） detection was constructed，under the external magnetic field through magnetic assembly of the MMINPs．The MMINPs were prepared by one-step method through miniemulsion self-assembly，with oleic acid modified magnetite nanoparticles as the magnetic cores，the amphiphilic random copolymer P（St－,co,－VP） as both the emulsifier and coating，and TC as the template molecule．PVP molecular chain stretched outward to obtain a steric hindrance between magnetic colloidal nanoparticles（MCNPs） owing to the hydrogen bonding between the PVP and water molecules．A magnetic responsive photonic crystal based on steric hindrance rather than electrostatic interaction as the counterbalance to magnetic attraction was developed．During the self-assembly of the P（St－,co,－VP） aggregating on the surface of MCNPs，the target molecules were added，which were imprinted in the coatings of MCNPs，relying on the hydrogen bond between PVP and the templates without further polymerization reaction．The MMINPs was characterized by transmission electron microscopy（TEM），Fourier transform infrared spectoscopy（FT－IR） and thermal gravimetric analyzer（TGA）．In FT－IR spectrum for MMINPs，the stretching vibration peaks of C—O indicated the successful imprinting of TC．TEM showed that the particles were regularly spherical and uniform in size distribution．The average particle diameter of the MMINPs was around 153.6 nm．TGA showed that the content of magnetic substance was high to 67.44%，which was ascribed to ferromagnetic substance （Fe,3,O,4, or Fe,2,O,3,） with high thermal stability．The preparation conditions of TC－MMINPs were optimized and the sensitivity，response time and the selectivity of TC－MMIPCs sensors were also investigated．With the increase of concentration from 1.0 × 10,-4, g/L to 1.0 g/L，the reflection wavelength of TC－MMIPCs redshifts from 500 nm to 578 nm．The logarithm of the concentration of TC exhibits a linear relationship with the reflection wavelength in this range．The detection limit（,S,/,N ,= 3） was 1.0 × 10,-4, g/L and the response equilibrium time of the TC－MMIPCs sensor did not exceed 30 s．Such a rapid response was attributed to the surface imprinting．The imprinting factor of the TC－MMIPCs was 3.41 and the response was specific with the selection factor of 5.92 for chloramphenicol，which is structurally similar to the tetracycline．TC－MMIPCs were successfully applied to determine TC in the actual samples．A brand of soothing moisturizing spray was analyzed，the TC content in the moisturizing spray was obtained based on the linear curve of the TC concentration and the reflection wavelength obtained previously，and no TC was detected in the moisturizing spray.