With potato variety Dongnong 311 as test material,the 3414 fertilizer experiment design was adopted to researches the relationship among SPAD value of top three leaves in main potato growth stages,fertilizer application and relative yield.The experimental results showed that SPA D value was significantly and positively correlated with nitrogen and potassium applied.But it was negatively related to the quantity of phosphorus.To a certain range of Nitrogen level,it was positively related to the relative yield.The fitting equation only under the influence of the nitrogen showed that at potato tuber formation stage critical SPAD value was 45.16,at the tuber enlargement stagecritical SPAD value was 44.00,and at the starch accumulation stage the critical value was 44.14 SPAD.