The accurate formula of helical gear’s contact line length is derived

and then its changing law and dynamic statistical law of meshing process are analyzed

the dynamic stat istical law of the contact line length change curve are obtained and simulated.The best and the worst condition of combination for transverse contact ratio and overlap rat io are given.Finally

based on the MATLAB programming algorithm

the variable helical gear contact line length calculation and parametric adjustment are realized

the conclusions have a certain theory signif icance and practical value for the helical gear transmission design.Key words Helical gear Contact line length Contact ratio MATLAB