Abstract: 【Objective】 The demand for the pecan cultivar ‘Pawnee'(pro)is high in China. However, its heterodicogamous often cases unstable yield. Studying the process of flower differentiation is essential for the adjustment of the flowering period and balance year's production. 【Method】We combined phonological observation with photographs of paraffin sections to study the developmental progress during flower differentiation; we observed ‘Pawnee''s(protandrous)fruiting bud differentiation and the growth of female and male gametophytes. 【Result】We established a connection between external morphology and internal anatomy during development. Male pecan flower budding initiates in early April; this is then followed by the inflorescence differentiation stage, stamen differentiation stage, sepal primordium differentiation stage, stamen growth stage, anther develop stage, and pollen sac and pollen formation stage. The corresponding morphological changes included: male flower buds changed from green and soft to brown and hard, the buds swelled, male flower bud scales cracked, inflorescence elongated, flower bracts swelled and cracking, then anther turn to yellow. The female flower buds began to develop from a terminal branch since mid-April. They then entered the critical period of morphological differentiation as follows: pistillate inflorescence differentiation stage, flower stalk and flower primordium differentiation phase, perianth primordium stage, bract primordium differentiation phase, sepal differentiation stage, pistil differentiation stage, and ovule differentiation stage. The corresponding morphological changes included: female flower bud scales changed from yellow green to brown to gray green, the scales gradually opened, flake off epidermis, floret primordium appeared swollen, exposing the stigma and style of elongation. Thus, it is feasible to judge the period of pecan flower differentiation based on flower buds' morphology and anatomical structure preliminary.