Abstract: In order to study the regularity of floor heave deformation and instability of soft rock roadway under different horizontal stress boundary conditions, the return air roadway of 50213 working face of Guantun Coal Mine was taken as the engineering background. According to the failure characteristics of floor in soft rock roadway, the mechanical model of floor structure in soft rock roadway is established by using the pressure bar theory. Through mechanical analysis, the distinguishing conditions of floor instability and the calculation method of critical stress are determined, and the calculation formula of floor heave is derived by using the deflection equation of floor rock deformation. The failure mechanism of floor and the dynamic evolution process of cracks under different stress states were determined by similarity simulation, and the floor heave control method of rock-concrete composite structure was put forward and applied in field practice. It can be concluded that when the loading is 3.13 MPa, the stress concentration zone is formed on both sides of the roadway and transferred to the floor through the two sides. The shear fracture develops from the interior of the wall rock along the roadway wall to the interior of the floor. The fracture is 0.8 m away from the two sides and the development Angle is about 45°.When loaded to 4.38 MPa, the floor bends and deforms towards the roadway surface under the action of horizontal stress, and tensile cracks occur in the middle of the floor. When the stress is loaded to 7.70 MPa, the failure depth of the floor increases to 1.2 m and the number of cracks increases. Due to the different deflections of each layer of the floor, it is easy to produce stratification cracks, and the cracks are connected with each other and extend deep. The maximum floor heave is 0.51m, which is basically consistent with the theoretical calculation results. 50213 face return air roadway floor heave is mainly caused by the rock and stress concentration, thus put forward the concrete combination with anchor rod structure to control the floor heave prevention measures, experimental section observation results show that the average speed of floor heave of 16 days tend to be stable, the sole drum quantity is 0.153 m, is not supporting to reduce 73%, floor control effect is better, The validity of supporting parameters is verified.