By taking a high speed printing machine as a study example,on condition that allowable pressure angle is satisfied,there is a corresponding maximum value（β,m,）,max,of travel angle of rocker βmexist when an appropriate initial angle of rocker θ50 is given,according to this,whereby search,the optimal initial angleθ*50,（β,m,）,max,*and（β,m,）,max,value domain-( 0,（β,m,）,max,*]are solved. The connotation of the mechanism dimension synthesis task of high speed printing machine is enriched and expanded. It has important theoretical value and practical engineering significance to design better and optimal dimension parameter mechanism.