The invention relates to a preparation method of a coal-series reservoir group fracturing object model sample taking a transition zone into account. The preparation method includes the steps: uniformly mixing cement and quartz sand according to a certain proportion, adding water, stirring the cement, the quartz sand and the water to form cement slurry, and pouring the cement slurry to the bottom of a sample mould to form a rock layer of a coal-series reservoir group; uniformly mixing the cement, the quartz sand and pulverized coal according to a certain proportion, adding water, stirring the cement, the quartz sand, the pulverized coal and the water to form coal-bearing slurry, preparing at least ten parts of coal-bearing slurry containing different proportions of pulverized coal, pouringthe coal-bearing slurry to an intermediate layer of the sample mould layer by layer according to the sequence from small proportions of the pulverized coal to large proportions of the pulverized coalto form the transition zone of the coal-series reservoir group; uniformly mixing the cement, the quartz sand and the pulverized coal according to a certain proportion, adding water, stirring the cement, the quartz sand, the pulverized coal and the water to form coal-bearing slurry, pouring the coal-bearing slurry to the top of the sample mould and inserting a plurality of mutually perpendicular paraffin slices to form a coal and rock layer of the coal-series reservoir group. The mechanical property of the object model sample prepared by the method is infinitely close to that of the real coal-series reservoir group.