Abstract: In order to understand the effects of potassium rates and density on potato yield and commodity rate, a field experiment was conducted under plastic covering. Two factors each set three levels, randomized block arrangement, potato of‘ZhongShu NO.3’was supplied. The results showed that: there was very significant difference between different potassium rates (P＜0.01), A2 (K₂SO₄ 375 kg/hm²) > A3 (K₂SO₄ 225 kg/hm²) > A1 (K₂SO₄ 525 kg/hm²), the theoritical K application rate for gaining maximum yield was 367.5 kg/hm². There was very significant difference between different planting density (P＜0.01), B1 (63000/hm²) > B2 (69000 /hm²) > B3 (78000/hm²). There was a negative correlation between the potato yield and planting density, within the planting density of 63000/hm²-78000/hm². The theoritical planting density for gaining maximum yield was 63000/hm². The optimal combination for the maximum yield (17577.7 kg/hm²) was A2B1, with K₂SO₄ 375 kg/hm² and planting density of 63000/hm². The commodity rate of different potassium rates was A1 > A2 > A3, the commodity rate decreased with the reducing of potassium rates. The commodity rate of different planting density was B1 > B2 > B3, the commodity rate decreased with the increasing of potassium rates. The theoritical potassium application rate for gaining maximum yield was 367.5 kg/hm². The optimal combination for the maximum commodity rate (68.4%) was A1B1, with K₂SO₄ 375 kg/hm² and planting density of 63000/hm².