目前我国降税减费政策有利于为企业提供宽松的营商环境，但已有的增值税税率设定，可能导致小规模纳税人降低销售额以达到降税目的，所以有必要探究我国增值税体系对小规模纳税人的行为影响。本项目将基于群聚（bunching）方法探究（1）小规模纳税人和一般纳税人的增值税税率差异对小规模纳税人销售额变化的弹性，以及（2）增值税起征点对小规模纳税人的行为影响，并进行福利损失分析。为了最大化社会福利，（3）本项目对我国增值税体系进行最优设计，将小规模纳税人加入在传统增值税模型中，确定小规模纳税人最优起征点及小规模纳税人和一般纳税人最优销售额阈，并进行模型参数的校准。（4）基于增值税最优起征点与最优销售额阈合理评估现有增值税政策在减税降费和新冠疫情背景下对小规模纳税人和小微企业的行为影响，为我国结构性减税与全面减税降费提供理论支持与政策建议。

The tax and fee reduction policy in China is conductive to providing a relaxed business environment for enterprises, but the existing VAT rate setting may lead to small-scale taxpayers to reduce sales to achieve the purpose of tax reduction, so it is necessary to explore the impact of China's VAT system on the behavior of small-scale taxpayers. Based on the bunching analysis, (1) this project will explore the elasticity of the difference of VAT rates between small-scale taxpayers and general taxpayers to the change of sales of small-scale taxpayers, as well as (2) the impact of the exemption of VAT on the behavior of small-scale taxpayers, and further analyze the welfare loss. In order to maximize social welfare, (3) this project designs the optimal VAT system, adds small-scale taxpayers to the traditional optimal VAT model, determines the optimal exemption and the optimal sales threshold for small-scale taxpayers and general taxpayers, and calibrates the parameters in the model. (4) Based on the optimal exemption and optimal sales threshold, this project reasonably evaluates the impact of existing VAT policies on the behavior of small-scale taxpayers and small enterprises in the context of tax and fee reduction and the spread of novel coronavirus, and provides theoretical support and policy suggestions for structural tax reduction and comprehensive tax reduction in China.