Underwater grouting method for deepwater jacket

The invention discloses an underwater grouting method for a deepwater jacket, which comprises the following steps of: S1, welding a pipeline launching roller at a water entering position of a gunwale of an operation ship, positioning the operation ship above a grouting opening of the jacket, and enabling a grouting pipeline to enter water at an approximately vertical angle; s2, the grouting pipeline starts to be externally placed, and when the grouting pipeline enters water by a certain distance, the deepwater compensation crane of the workboat is used for lowering the grouting pipeline to the position close to a grouting opening of the jacket all the time; s3, the grouting pipeline is connected with the grouting opening through movement adjustment of the workboat; and S4, after cement paste work of the pile leg is completed and the grouting pipeline is cleaned, the workboat moves the grouting pipeline to the next grouting opening, and grouting continues after connection. The device can be suitable for underw