Exhaust gas purification system of internal combustion engine

To provide, in an exhaust gas purification system of an internal combustion engine that reduces NOx occluded in a NOx catalyst by decreasing a quantity of an exhaust gas flowing through an occlusion reduction type NOx catalyst and supplying a reducing agent to the NOx catalyst, a technology capable of improving dispersibility of the reducing agent into the NOx catalyst. Valves (12a, 12b, 13a, 13b) for adjusting a quantity of the exhaust gas are disposed upstream and downstream of an occlusion reduction type NOx catalyst(11a,11b). In a state where the first downstream-side valve(13a) disposed on the downstream side substantially minimizes the quantity of the exhaust gas flowing through downstream of the occlusion reduction type NOx catalyst(11a) and an reducing agent added from a first reducing agent adding valve(14a) exists in a first NOx catalyst(11a), the first upstream-side valve(12a) disposed on the upstream side changes the quantity of the exhaust gas flowing through upstream of the first NOx catalyst(11a). Then, the reducing agent existing within the occlusion reduction type NOx catalyst(11a) is dispersed throughout the catalyst due to a change, occurred on that occasion, of a flow state of the exhaust gas in the first NOx catalyst(11a).