Shared Values and Normal Families

In this paper the problem of normal families of meromorphic with relation to shared values has been researched,and the following result is proved:let F be a family of meromorphic functions in D,and a,b,c,d be four distinct finite complex values such that b≠0,c≠a and d≠b,and k be a positive integer.If for every f∈F,the zeros of f-c are multiplicity ≥k and f(z)=af(k)(z)=b,f(z)=c■f(k)(z)=d,then F is normal in D.This resut extends the normality criterion of Chang Jianming.