The invention relates to a preparation method of magnetic graphene aerogel. The preparation method comprises the steps of crosslinking dopamine modified graphene oxide with iron ions, carrying out heating reduction and self-assembling to form a three-dimensional graphene aerogel structure, and carrying out freeze drying and thermal treatment, so as to obtain a magnetic graphene aerogel material in situ. The preparation method which is simple in operation and preparation process and low in cost is utilized for preparing the magnetic graphene aerogel material with stable structure and good uniformity in situ and is a new technique for massively preparing the magnetic graphene aerogel material. The prepared material has good magnetic property, low density, good mechanical property, high temperature resistance, large specific surface area, super-strong adsorptive property, conductive property and wave absorbing property, is hopeful to be used as a novel functional magnetic material in the fields of water treatment, photoelectric materials, wave absorbing materials and the like and further has certain application values and market prospects.