Abstract: Grey incidence model determines the closeness degree from the closeness and similarity of statistical sequence's geometrical form.Traditional grey incidence model calculates statistical sequence's correlation degree from the perspectives of its acreage,slop e,changing velocity,etc.These incidence models have dual influences exerted by horizontal and vertical coordinates.Subsequently,inference of other factors occurs,when we analyze the relationship between statistical sequence's individual factors.To overcome this limitation,the paper proposes the degree of grey periodic incidence judged by slope,according to the winding situations of two curves,and judging wave period of the curve by calculating the slope of every polygonal line.The calculation is simple and intuitive on judgment by the method.It can not only solve effectively the problem of above reference,but also have good quality of traditional gray periodic incidence.At last,the paper validates its practicability with a practical case.

Key words: slope, grey, periodic, relationship model