Community structures and edaphon quantities play important roles in soil quality changes and nutrition cycling. Different fertilization patterns strongly affect community structure and edaphon quantity, as well as plant and cultivated land quality. However, there is little information about the soil microbial community and functional diversity that is affected by different potassium fertilizer sources on purple soil. To understand the effects of potassium sources and rates on crop yield and microbial community structure in the Chongqing region, a four-year (12 seasons) experiment was conducted on a purple vegetable soil with a rotation of lettuce-cabbage-sweet corn. There were seven treatments consisting of a control (CK, no potassium fertilizer), low dose of chemical potassium fertilizer (K₁), medium dose of chemical potassium fertilizer (K₂), high dose of chemical potassium fertilizer (K₃), low dose of straw (M₁), medium dose of straw (M₂), and K₁+M₁. Crop yields, soil microbial properties including contents and composition of microbial phospholipid fatty acids (PLFA), the microbial community, and the ratios of microorganisms were investigated. Results showed that application of two types of K fertilizer sources increased the yield of lettuce, cabbage, and sweet corn when applied at 300 kg·N hm^-2 and 150 kg·P₂O₅ hm^-2. The treatments of K₂, M₂, and K₁+M₁ effectively promoted cabbage yield by 28.05%-30.27%. The treatments of M₂ and K₁+M₁ effectively increased lettuce yield by 13.89% and 13.81%, respectively, whereas the K₁+M₁ treatment effectively enhanced sweet corn yield by 15.10%. These results elucidated that the K₁+M₁ treatment appeared to be an effective combination for production of these three crops. The PLFA analysis of soil microbes showed that different potassium sources affected the soil microbial community structure and abundance. The K₁+M₁ treatment improved the content of bacteria, fungi, and gram-positive bacteria, and thus significantly increased the total PLFA content and mitigate environmental stress imposed on microbial survival. It further illustrated that the application of corn straw with a small amount of chemical potassium fertilizer (K₁+M₁) could create a favorable environment for the growth and reproduction of soil microbes. Correlation between the average yield of three crops (lettuce, cabbage, sweet corn) and the content of soil microbes (bacteria, fungi, gram-positive bacteria, and gram-negative bacteria) was significant (P < 0.05), whereas different K sources and rates affected soil microbial characteristics. Thus, K fertilizer might increase crop yield by regulating soil microbial characteristics.