Abstract: An exhaust gas treatment system includes: confirming that an engine stops operation; sensing present pressure difference between front and rear sides of an EGR value; setting learning value by performing large offset learning, if the present pressure difference exceeds an absolute value of a first lower or upper values; setting learning value by performing step learning, if the present pressure difference exists between first and second lower values that is larger than the first lower value or the present pressure difference a between first and second upper values that is smaller than the first upper value; and setting the present pressure difference value as a learning value, if the present pressure difference exists between the second lower and second upper values. The exhaust gas treatment method accurately learns the pressure difference of the EGR system to improve the quality of the exhaust gas and securely control the EGR system.