A potted experiment was carried out about tomato of ‘Jinpeng No.10’ in temperature and potassium fertilizer interaction to explore the effects on photosynthesis and quality in greenhouse.The results show that,compared with the normal temperature,the sub-low temperature keeps the greenhouse tomatoes grow slowly,and ni flowers number,leaves number,internodal length,chlorophyll content,net photosynthetic rate,stomatal conductance,the intercellular CO₂ concentration,transpiration rate,stomatal conductance,water use efficiency,weight and quality decreased obviously,and stomatal limitation increase.But if add a certain amount of potassium fertilizer,it can remit the harm of the greenhouse tomatoes,and improve flowers number,leaves number,internodal length,chlorophyll content,photosynthesis,tomato fruit weight and quality under the sub-low temperature.Under the sub-low temperature stress,as the dosage of potassium fertilizer for one sample is 18.54 g has conspicuous impact on alleviating the harm of tomato plants.Less or more is not good for the tomato plants.In summary,adding a certain amount of potassium fertilizer can improve tomatoes’ the ability of resistance to the sub-low temperature stress;it benefits the tomatoes plants’ growth and fruit quality.