The objective of this study is to investigate the effect and mechanism of straw biochar on disease control of Phytophthora blight of chilli pepper. The effects of straw biochars produced at two pyrolysis temperatures on disease control of Phytophthora blight of chilli pepper was studied with pot experiment. Soil physicochemical properties, soil microbial population and structure, Phytophthora capsici density and plant physiological and biochemical indexes associated with disease resistance were determined. Straw biochars produced at 500℃ and 600℃ both showed a good control efficacy against Phytophthora blight, while biochar produced at 500℃ had a better control efficacy than that produced at 600℃. In addition, biochar produced at 500℃ also promoted the growth of chilli pepper. Biochar treatment significantly increased content of total N, available P and available K of soil, especially available P. Both biochars not only enhanced the population of culturable microorganisms, especially fungi and actinomycetes, but also increased the diversity of soil microbe and changed the dominant microorganisms. RT-PCR analysis showed that biochar treatment increased the population of bacteria in soil inoculated with P. capsici, but had different impacts on fungi population. Although biochar increased the number of pathogens of P. capsici, there was no disease incidence. Plant physiological and biochemical indexes showed that the control effect of biochar on disease was not related to disease resistance induced by the biochars. Application of straw biochar reduced chilli pepper blight incidence greatly, and improvement of soil nutrient condition and microbial community structure might be one of mechanisms for disease suppression.