The method to obtain tumor cells from the primary culture of xenograft is commonly used. As primary culture is distinct from usual culture of single-layer cells, it also follows different patterns of cell growth. In order to observe the cell growth law of xenograft, a cell line (293-BAC) which stably expressed GFP was firstly used to formed transplantation tumor in nude mice. Primary culture of the tumor tissue was then conducted. Due to the stable GFP expression in the 293-BAC cells, the cell growth was observed through GFP readout and by analyzing the morphology of the cells from tumor tissue. Tumor cells in the masses of tissue were released to the out rim, gradually extending to the vicinity space. Cells in thin pieces which were scattered during planting were able to adhere to the flask wall and directly grew. There were about 1%～3% of mouse-origin cells growing among the tumor cells or gathering at the outskirt of newly-grown tumor cells. The mouse-origin cells disappeared after 5 passages of subculture. After the process of tumor forming and serial subpassages, the tumor cells were pure-sourced with stable growth property, thereby becoming good material for further research. Cell growth patterns of reference value for transplantation tumor or related research were provided.