A low pressure EGR valve is controlled by mixing EGR gas into an intake air. Steps of the method include detecting temperature and pressure of an intake air passing through an air cleaner, detecting temperature and pressure of the intake air at a downstream side of an intercooler, detecting temperature and pressure of an EGR gas at an upstream side of an EGR cooler, determining a control duty of the low pressure EGR valve on the basis of the detected temperature and pressure of the air passing through the air cleaner, the detected temperature and pressure at the downstream side of the intercooler, and the detected temperature and pressure at the upstream side of the EGR cooler, and controlling the low pressure EGR valve based on the determined control duty. An apparatus for executing the method is also provided.