Simulationg of phasic development in wheat is necessary in constructing wheat growth and yield models. It is also useful for evaluating culvivar adaptation and scheduling cultural practices. This paper describes a conceptual model of wheat development based on phenological principles, as affected by vernalization, photoperiod, thermal response and intrinsic earliness, and also reports the results of ensitivity analysis and validation of the model. The model predicts when the plant will reach double ridge, termianl spikelet and heading. In tthe model, the daily thermal sensitivity of development following emergece is determined by and interacton of relative vernalization comptetion and relative photoperiod effectiveness for that day. After complete vernalixation is reached, the daily thermal sensitivity is determied only by relative photoperiod effectiveness, which gradually increases from terminal spikelet to heading. A multiplication between the daily thermal sensitivisty and thermal effectiveness generated daily flowering were characterized as vernalization requirement, photoperiod sensitivity and intrinsic earliness. The model showed a sensitive response to environmental varibles of temperature and daylength. and to gentic parameters of vernalizaion requrement and photoperiod sensitivity. Evaluation of the model using multiple experimental data involving varous cultivars and planting dates exhibited a marked goodness of fit between simulation and observation with a root mean square error<5 days. The results indicate that the model can be used a prdictor for the major flowering stages. as well as functioning as dnowledge for understading the characteristics of different develoment componcets in wheat.