The utility model discloses an underground dart-type blocking tool used for a coiled tubing. The blocking tool comprises a dart mechanism and a work barrel mechanism, wherein the dart mechanism comprises a first upper connector, a mandrel and a guide shoe, the first upper connector is fixedly arranged at the upper end of the mandrel, the guide shoe is fixedly arranged at the lower end of the mandrel, the mandrel between the first upper connector and the guide shoe is provided with a first locking structure, and the mandrel between the first locking structure and the guide shoe is provided with a first sealing structure; the work barrel structure comprises a second upper connector and a plug, the inside of the second upper connector is provided with a second locking structure matched with the first locking structure in locking, the inner wall of the second upper connector on the lower portion of the second locking structure is provided with a second sealing structure matched with the first sealing structure in a sealed mode, and the plug is located in the second upper connector and is fixedly arranged at the lower end of the second upper connector. A coiled tubing speed string can be taken out in a pressure state, primary well killing is unnecessary, and the amount of working solutions entering a stratum is substantially reduced.