The utility model provides a gaseous middle -jiao oil assay structure and prevent jam system thereof, including gas -supply pipe and blast pipe, gas -supply pipe, blast pipe are through at least a setof condensing pipelines intercommunication, condensing pipelines includes and is provided with the condenser pipe in the condensation container by the condensation container, the both ends of condenser pipe respectively with intake pipe and outlet duct intercommunication, intake pipe and gas -supply pipe intercommunication, outlet duct and blast pipe intercommunication, be equipped with first valve in the intake pipe, be equipped with the second valve on the outlet duct, the condenser pipe includes at least one collection section, and the condenser pipe of collecting the section is the ascending sunken form of opening, the minimum department of collecting the section condenser pipe has seted up the tar discharge port, and the bottom of tar discharge port is equipped with tar and collectsthe container, and tar is collected the container and is placed on the weighing device. The utility model discloses quantity of gas and tar quality can accurate measurement await measuring to the tarcontent in the gas that awaits measuring is measured to the accuracy, simultaneously the tar composition in the gas of awaiting measuring can be effectively got rid of, the interior jam of condenser pipe is prevented.