Abstract: Doubly-fed variable speed pumped storage is the new development direction of pumped storage technology all over the world because of their advantages such as quick adjustment, high efficiency, flexibility and reliability. However, there is no operational doubly-fed pumped storage plant in China. The study of the dynamic characteristics and control strategy of variable speed units relies on numerical simulation without operation data support and measurement verification. The no-load characteristic of VSPSU was analyzed and the evolution mechanism of variable-speed operating point was revealed by model experiments of different heads and rotating speeds based on the VSPSU experiment platform. The migration distance and operating point slope were put forward to quantify no-load performance. The novel quick start strategy for VSPSU is further proposed and integrated into the monitoring system. The operation results show that the proposed strategy could break through the constraints of the "S" characteristic region and the grid-connected synchronous zone, save the normal starting time by 47.87%, and reduce the maximum amplitude of pressure pulsation by 45.54%. The difficulty of grid connection caused by the fluctuation of no-load frequency in low head conditions could be fundamentally solved.