Comparison in income taxes paid by medium-income class was made among China, America and Great Britain, the main purpose of which is to deduce the level of poverty line and the level of income that should pay tax. A function of the level of income that should pay tax and the average tax rate was established. The conclusion is that as far as the tax rates of medium-income class in the three countries are concerned, China's is almost the same as America's, but China's is quite lower than Great Britain's