Abstract: The way of Bishop can be used to obtain the radius of slope,which needs to input a first coordinate of a circle center and the radius,needs many experience and even needs many times inputting.Obviously it leads to many troubles.By the way of producing random datum,the paper opens the whirlpool(linepool),puts forward the method of searching safety factor on Monte Carlo-grads,and concludes that the connection between the safety factor and the beginning radius is close.