税务机构的税收执法力度无疑是影响企业避税的重要因素，但是该研究领域面临两个主要的障碍：一是无法获得企业层面上的税收执法力度，二是税收执法与企业避税互为因果，造成内生性难题。本项目以中国2002年的所得税分享改革为自然实验，以国税局和地税局差异化的税收激励为条件，在企业维度上识别了由外生改革冲击带来的税收执法力度变化，从而解决了税收执法力度的识别难题；基于1998-2007年大样本的微观企业数据，利用账面-应税收入差异法和实际税率法测算了企业避税，采用断点回归设计方法研究税收执法力度对企业避税的影响，通过安慰剂检验等方法规避其他政策的干扰，以获得稳健的结论；研究避税的企业是否会相应增加固定资产投资或研发投资，以及这种效应是否会转化为企业的长期竞争力，如劳动生产率和全要素生产率；由于税收执法力度的调整属于地方政府策略性行为的范畴，本项目也为现阶段的结构性减税和相关的税制改革提供重要的政策启示。

Tax enforcement affects the tax avoidance behavior of corporates, but there are two challenges faced by the research, first is that the data of tax enforcement is unavailable, and secondly, the tax enforcement is endogenous to the tax avoidance. This project takes the Income Sharing Reform in 2002 of China as a natural experiment to identify the tax enforcement, the reform attributes firms to two tax agencies, National Tax Bureau and Local Tax Bureau which have different tax enforcement, according their established date. Based on large micro data from 1998 to 2007, we calculate the tax avoidance with two methods, book-tax difference and effective tax rate, then study the effects of tax enforcement on tax avoidance using Regression Discontinuity Design and get robust results by eliminating other possible policies with Placebo Test. We also study whether firms increase investment on capital or R&D when avoiding tax and the impacts on firms' long term competitiveness, such as labor productivity of total factor productivity. Since the change of tax enforcement is one strategic reaction of local governments, this project has policy implications on tax cut and tax reform.