Abstract: It has not yet been answered whether the solution of Swedish Method is the the lowest solution or under what condition it is the the lowest solution when the safety factor of the slope with the same circular slip surface is calculated.Some laws of the the lowest solution in the slice method was concluded on the basis of analysis of the relationship of the safety factors among Swedish Method,Simplified Bishop Method,Spencer Method,Simplified Janbu Method,Method of U.S.Army Corps of Engineers and Transmitting Coefficient Method.