Based on a project on shallow ultra-soft soil improvement in Gaolan seaport area in Zhuhai seaport, a field test trial area with different spacing of PVD was prepared. By field monitoring and testing, the impaction of PVD spacing on the soil improvement effect was analyzed in terms of the vacuum, the settlement and the geotechnical test parameters. It is concluded that: 1) When the PVD is constructed with a smaller spacing, the construction disturbance is bigger among the PVDs, but the improvement effect is not optimum; 2) According to the experiment and comparison, the optimum spacing of PVD is 0.8 m for this project; 3) After soil improvement, the thickness is more than 40 cm, satisfying the requirement of follow-up construction.