The invention discloses a preparation method of magnetic graphene oxide and a method for detecting naphthalene content in water by using magnetic graphene oxide solid-phase extraction. The preparation method includes: dissolving the graphene oxide in an ethylene glycol solution in a scattered manner for ultrasonic concussion; adding FeCl3.6H2O and NaOAc prior to mechanical stirring; putting mixed liquid into a teflon stainless reactor at the reaction temperature of 190-200DEG C for 5-6 hours of reaction; subjecting obtained samples to filtering and washing with plenty of water and ethyl alcohol prior to drying in an oven to obtain the magnetic graphene oxide. The detection includes the steps of mixing, solid-liquid separation, washing, elution and detection. The magnetic graphene oxide is simple and rapid in preparation technology, high adsorption capability of the graphene oxide on naphthalene can be fully utilized, the magnetic graphene oxide materials can be rapidly separated from sample solutions under the action of external magnetic field, dosage of the organic solutions is reduced, and high efficiency and environment protection are achieved; limit of detection of the naphthalene in water can be effectively improved.