We used tomato cultivar ‘184’ as material, adopting the tomato protected substrate cultivation mode of water and fertilizer integration, taking the potassium fertilizer in plant nutrient solution formula C of Gansu Agricultural University as the control T₁ (conventional potassium fertilizer amount), and then adding different amounts of potassium fertilizer to formula C to treat T₂ (potassium fertilizer increment 25%), T₃ (potassium fertilizer increment 50%), T₄ (potassium fertilizer increment 75%), To explore the effects of different potassium application rates on the growth, physiology, yield and quality of tomato cultivated in protected substrate, and to screen the best potassium application rate under the condition of protected substrate cultivation. The results showed that: (1) compared with the conventional potassium fertilizer application (T₁), the increased application of potassium fertilizer (T₂-T₄) can significantly increase tomato plant height, stem thickness, and root vigor, and all the indicators of T₃ treatment are the highest, while the effect of increasing potassium fertilizer on the number of leaves was not significant. (2) Compared with T₁, the potassium fertilizer treatment can significantly increase the photosynthetic pigment content in tomato leaves, enhance the photosynthesis and fluorescence process, and further promote the absorption and transformation of light energy, and the T₃ treatment has the highest increase. (3) With the increase of potassium application rate, tomato single fruit weight and fruit yield of increased potassium fertilizer treatments showed different degrees of growth trends. Appropriate increase of potassium fertilizer treatments reached a significant level, and the T₃ tomato yield was the highest, and significantly increased 20.87% production by T₁. (4) Compared with T₁, the hardness, total soluble sugar, Vc, soluble protein, and lycopene contents of tomato fruits in each potassium application treatment increased to varying degrees, and each index increased first and then decreased with the increase of potassium application. The trend of change and reach the optimal under T₃ treatment. (5) Principal component analysis shows that the comprehensive score of each treatment is T₃>T₄>T₂>T₁. The study found that under the condition of facility substrate cultivation, adding a proper amount of potassium fertilizer can significantly improve the photosynthesis efficiency of tomato plants, promote plant growth, and achieve the purpose of increasing fruit yield and quality. The effect of treatment with a 50% increase in conventional potassium fertilizer was the best.