The invention discloses an oilfield associated gas complete liquefaction recovery system and a method thereof. The system comprises, sequentially connected, an associated gas pretreatment apparatus, a heat regenerator, a first condenser, a gas-liquid separation device, a throttle valve, a second condenser, an LNG storage tank and a regulating valve, the associated gas pretreatment apparatus comprises, sequentially connected, an oil removal device, a dedusting purification device, an acidic gas removal device, a hydration device and a nitrogen adsorption and separation device, the light hydrocarbon outlet of the heat regenerator is connected with the regulating valve, and the lower portion of the gas-liquid separation device is connected with the light hydrocarbon inlet of the heat regenerator. Separating recovery of light hydrocarbons in the oilfield associated gas and liquefaction of natural gas are simultaneously realized by using cold energy provided with above two stage condensing heat exchange devices. The system and the method have the advantages of solving of the recovery problem of remote region oil and gas wellhead associated gas, convenient operation, low cost, high resource recovery rate, no pollution, realization of zero discharge in the oilfield oil extraction process, and obvious resource saving and environment protection effects.