The invention provides an online resin sampling device. The online resin sampling device comprises a resin separation tower, a negative regeneration tower and a positive regeneration tower, wherein one side of the resin separation tower is connected with a high-speed mixing bed through a first transmission pipe, a branched sampling pipe is arranged on the first transmission pipe, and a first sampling valve and a third sampling valve are arranged on the branched sampling pipe; the negative regeneration tower is located on the other side of the resin separation tower and is connected with the resin separation tower through a second conveying pipe with a second sampling valve; the positive regeneration tower is located on one side, far from the resin separation tower, of the negative regeneration tower and is connected with the resin separation tower and the negative regeneration tower, respectively through the branched sampling pipe, and the third sampling valve is located between the negative regeneration tower and the positive regeneration tower. The invention further provides an online resin sampling method utilizing the online resin sampling device. The resin is sampled in each stage by virtue of the first sampling valve, the second sampling valve and third sampling valve. According to the device and the method, the resin can be sampled without opening a manhole door of a tank body or a bed body, so that the operation is convenient.