The effect of temperature and photosynthetic photon flux density on in vitro growth of Oncidium plantlets was studied to develop a growth model for tissue culture of plantlets. The dry weight of plantlets served as the growth index to validate the model. The growth models were developed and validated by nonlinear regression analysis, and then growth parameters of models were further studied. The experimental result validated the growth model. High temperature and high photosynthetic photon flux density treatment gave the highest dry weights for four treatments during the same culture days. The results provide useful information for the propagating of Oncidium plantlets.