So far the problem of determining the width of normal line for pebble shoals has not beeen completely solved.Inordect answerthe question. briefly describes the expressions of initiation condition of sediment movement. and further states the relationship between regulation of pebble shoal and initiation condition of sediment movement.Oa the basis of the concept of starting drag force the formula (15) and (16) for cilcalating the width of normal line to the gravel shoals are dsiuced by using the shield's formula and the Shields's curve and its modification,and then aeeding to the coacept of starting velo-city, we deduce the formula (19), (21), (21) and (22) respectively by use of the Zhang Ruijin's formila,the Tang Cunben's formila the Dou Guoren'sformula and the Sha Yuqing's formila.Finally,these formilas are compared by the measured data in the upper revenes of the Beijing River,The compirison results show that the calculated values of the formala (16) are in good agreement with the actual application values. It is expected that the formula can be served as a reference for channel regulations.