73 field trials of potassium fertilizer (K) application on winter rapeseed were conducted in rapeseed production regions of Anhui Province during 2005 to 2009 to study the effect of K application on rapeseed yield and profit. The abundance and deficiency indices of soil available potassium were determined based on the relationship between rapeseed relative yield and soil available potassium. The results showed that K application significantly increased rapeseed yield compared with control treatment. The average values of rapeseed yield, and increment and increase rate of the yield were 2 558 kg/hm², 509 kg/hm² and 28.1%, respectively. The net profit was 1 349 Yuan/hm² with K application and the value cost ratios were higher than 2.0 at 67.1% of the field trails. While at 13.7% of the field trails, rapeseed yield increased by K application, but farmers’ income was not increased. The rapeseed yields of the K application treatment were compared with that of control to obtain the relative yields, then the relative yields of <60%, 60% ~ 75%, 75% ~ 90% and >95% were selected to establish the abundance and deficiency indices for soil available potassium. The land areas of extreme deficiency, deficiency, slight deficiency, optimum and abundance indices of K occupied 2.7%, 17.8%, 65.8%, 6.8% and 6.8% of total area for winter rapeseed in the province. The extreme deficiency, deficiency, slight deficiency, optimum and abundance indices for soil available potassium were ＜30, 30 ~ 60, 60 ~ 110, 110 ~ 140 and ＞140 mg/kg, respectively. The soil available potassium critical indices can be used as guidance for potassium fertilization on winter rapeseed in Anhui Province.