Control method of exhaust gas purifying system

A control method for an exhaust gas purifying system installed in an exhaust gas passage of an engine and having a NOx occlusion reduction type catalyst including a catalyst metal and a NOx occluding substance, comprising:

• performing a lax rich control when the NOx occlusion reduction type catalyst is heated to a sulfur purge temperature or above, to control an air/fuel ratio of exhaust gas to a value equal to or slightly lower than a theoretical air/fuel ratio, wherein the lax rich control brings the an excess air factor of the exhaust gas to 0.95 to 1.0;
• and
• restoring the NOx occlusion reduction type catalyst from a sulfur poisoning, wherein a regeneration control is performed for restoring NOx occlusion capacity of the NOx occlusion reduction type catalyst to bring the excess air factor of the exhaust gas to 0.8 to 0.95 at an inlet of the NOx occlusion reduction type catalyst.