Abstract: The paper adopts the method of Numeral Statistic to estimate the range of the thickness based on a great deal of the datum of bore holes in-situ which can reduce the effect of the coal thickness as regionalized variable, takes the throughput of dragline as a variable, puts forward the concept of the dragline's production reliability on the condition of the change of coal seam thickness, establishes the model of machine-nature reliability of dragline-coal seam thickness, and defines the formula of calculating the value of reliability, which gives a valid method of researching the reliability of dragline-coal seam thickness.