A control method for a low pressure exhaust gas recirculation (LP-EGR) system may include measuring an engine speed and load, setting a target pressure difference between a downstream side and an upstream side of a LP-EGR valve according to the measured engine speed and load, measuring a present pressure difference between the downstream and upstream sides of the LP-EGR valve, comparing the present pressure difference with the target pressure difference, and preventing a reverse flow of a recirculated exhaust gas by adjusting an opening rate of the LP-EGR valve to alter a recirculated exhaust gas amount when the present pressure difference is smaller than the target pressure difference. The LP-EGR system for preventing reverse flow of a recirculated exhaust gas may include an air intake line, an exhaust line, a LP-EGR line, a LP-EGR valve, pressure sensors and a control portion.