【Objective】The objective of this study is to explore effects of saw dust ash ameliorating acid purple soil relative to dosage of the ash used, in an attempt to work out a scientific basis and reasonable measures to remedy degraded and acidified purple soil and hence to realize sustainable development and circular agriculture. 【Method】In this study, saw dust ash used was residue after combustion at 800~900 °C. A one-year field experiment was designed to have seven treatments different in saw dust ash application rate, i.e. 0, 3 000, 6 000, 9 000, 12 000, 15 000, 18 000 kg hm-2, and carried out in the Baishiyi Vegetable Base of Jiulongpo District, Chongqing, China, to explore effects of application of the saw dust ash on amelioration of acid purple soil, and on soil microbiota, soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN). 【Result】Results show: 1) application of saw dust ash increased yields of the vegetables significantly, showing a trend of the yield increasing with rising application rate; and the treatment applied with 18 000 kg hm^-2 of saw dust ash was 76.1%~121.9% higher than CK (0 kg hm^-2 applied) in vegetable yield; 2) Application of saw dust ash increased the content of organic matter and pH in the surface and subsurface layers of the degraded purple soil, and the effect was particularly significant in the treatment applied with 18 000 kg hm^-2 of the ash. However, overuse of the ash (over 18 000 kg hm^-2) had a negative effect on the content of exchangeable H+ and Al³⁺, while in the treatments applied with 12 000~15 000 kg hm^-2 of the ash no such effect was observed, and the content of exchangeable H⁺and Al³⁺ was 0.19~0.20 and 0.63~0.67 cmol kg^-1, respectively; 3) In the treatments applied with 12 000~15 000 kg hm^-2 of the ash, soil alkalytic N and readily available K increased significantly and in the treatment applied with 18 000 kg hm^-2 of the ash soil available P was the highest or 55.3 mg kg^-1 higher than in CK; And 4) The population of bacteria was the highest in the surface and subsurface layers and followed by that of fungi and actinomyces, and they peaked in the treatment applied with 12 000, 9 000 and 6 000 kg hm^-2 of the ash respectively. Compared with CK (A0), the treatments applied with 12 000~15 000 kg hm^-2 of the ash was significantly increased or by 70.4%~78.7% in SMBC content, and the treatment applied with 18 000 kg hm^-2 of the ash was the highest in SMBN content, reaching up to 40.54 mg kg^-1 and followed by the treatment applied with 9 000 kg hm^-2 of the ash, which was 34.32 mg kg^-1. 【Conclusion】Results show that application of saw dust ash can increase soil available nutrient contents, remedy soil acidification and improve soil microbial communities, SMBC and SMBN. In the study, the application rate of 12 000~15 000 kg hm^-2 is the most suitable one that can improve soil fertility and increase soil microorganic population in degraded purple soil.