This study inves tigates the effects of Tax avoidance on Tax risk using a conceptual and statistical modeling of Tax risk measuring, based on uncertainty indicator. The sample consists of 114 firms in the period from 2009 to 2016. Tax avoidance is measured by the effective Tax rate (ETR). Also Tax risk is measured using the EGARCH model and defined as the instability of Tax status over time. The research findings show that there is a significant negative relation between effective Tax rate and instability of the Tax status, which means that firms with lower effective Tax rate have instability of Tax status over time. On the other hand, findings indicate an increase in Tax difference in event of effective Tax rate decreases. According to findings, one of the consequences of Tax avoidance is increases of Tax risk. The findings provide new evidence about the consequences of corporate Tax avoidance. These findings can be used to assess the Tax risk of firms based on their effective Tax rate. Also the findings suggest investors and managements to consider the consequences of corporate Tax decreases.