In order to elucidate the dynamic changes of the mineral elements in leaves of 12-year old mature pecan trees’ bearing branches and provide a scientific basis for tree nutrition diagnosis and reasonable fertilization in future,we tested nine elements(N,P,K,Ca,Mg,Fe,Cu,Zn,Mn) by the Kjeldahl method,Mo-Sb colorimetry and atomic absorption.The results showed that:(1)The contents of different macro-element in mature leaves of pecan ‘Mahan’ were put in the following order:N＞K＞Ca＞Mg＞P,while the contents of different micro-element were put in the following order:Mn＞Zn＞Fe＞Cu.(2)The mature leaves’ absorption of mineral elements had obvious seasonal features:N,P,K and Cu were needed greater during the pollination flowering period,as well as N,P,K were needed more during the flushing period and fruit expanding period;the absorption of K,Zn,Mn had a tendency to continue to increase during the fruit growth period.(3)The contents of mineral elements in leaves were fluctuated according to time lapse.For macro-element,the fluctuation was small,but for micro-element,the fluctuation was noticeable large.The conclusion is that the appropriate period for analyzing the standards of nutrition diagnosis in pecan leaves is from July 27th to August 13th.It is recommended that N,P,K and Ca,Mg,respectively as primary and secondary base fertilizer should be added in the pollination flowering period and the flushing period,while organic fertilizer should be deep fertilized before the harvest of autumn fruit.