The material of the upper layers of the mining site is one of the factors that affects the rate of ground subsidence. During mining, the instability of the key layer plays a fundamental role in ground subsidence. Therefore, identifying the main key layer is of great importance. The main objective of this research is to evaluate the effect of various geometric and resistance parameters of the key layer, including its distance from the mined face, angle, thickness and resistance, on the rate of ground subsidence based on the finite difference method and using FLAC3D software. The results of the numerical models examined have shown that with increasing the distance of the key layer from the top of the mined site, the rate of subsidence directly increases. Also, with increasing the angle of the key layer relative to the mining site, the rate of subsidence decreases and the depression of the subsidence profile becomes asymmetric and tends towards the coal bases, which reduces the maximum settlement rate. In addition, as its thickness and strength increase, the ability of the key layer to absorb greater displacements and not fail increases, which is the reason why the settlement rate decreases.