The treatment of soft soil subgrade in reclamation site area is a difficult problem in land reclamation highway engineering. In response to the failure of high-pressure rotary jet grouting piles and the inability to extract cores during the construction process of a coastal highway project, and combined with the analysis on the geological and relevant quality inspection test, a soft foundation treatment method for combined grouting reinforcement of high-pressure jet grouting piles is proposed. The test pile results show that after using this method for soft soil foundation reinforcement, the average unconfined compressive strength of high-pressure rotary jet grouting piles after 120 days is 1.81 MPa, the core rate is not less than 90%, and the foundation bearing capacity is not less than 200 kPa. It can be seen that the combined treatment method of high-pressure rotary jet pile and grouting can effectively improve the construction quality of the pile body, and reduce the settlement of the foundation. The construction parameters and techniques used for the test pile can provide reference for the treatment of similar soft soil foundations.