This article starts with analyzing that influences the three main factors of the difficulty degree of the course,has structured a model N =α(S/T)+(1-α)G/T which portrays the degree of difficulty of course,and as the example with typical themes(namely knowledge one) in course of the geometry of stage of compulsory education,has made a concrete analysis of the whole degree of difficulty of course of these themes.The study on appraisal field of course of the method that this text puts forward will be inspired.