The invention relates to a long-tube liquid filling device and a method for filling liquid materials in a material jar into a container. The long-tube liquid filling device comprises a liquid-infusing tube, a fluid valve, an airflow channel and an air valve component for connecting/disconnecting the airflow channel, wherein the airflow channel comprises an air-return channel which is connected tothe container by pointing at the internal of the container from a container opening at the filling position after passing through a liquid outlet, a pressure-releasing airflow channel connected to a pressure-releasing chamber, a backpressure airflow channel connected to a backpressure air chamber and a liquid outlet connecting channel which is connected to the liquid-infusing tube by pointing at the internal of the liquid-infusing tube from the upper end of the liquid-infusing tube after passing through the liquid outlet. The air valve component comprises a pressure-releasing valve which can be switched on/off to connect/disconnect the air-return channel with/from the pressure-releasing airflow channel, a filling valve which can be switched on/off to connect/disconnect the air-return channel with/from the backpressure airflow channel, and a return valve which can be switched on/off to connect/disconnect the liquid outlet connecting channel with/from the pressure-releasing airflow channel.