Low temperature superconducting gravity gradiometer is the most sensitive equipment of measuring gravity. With mechanically levitated test masses and commercial SQUIDs, differential acceleration sensitivity of 10-12 m s-2 Hz-1/2 was demonstrated thirty years ago and is still the highest sensitivity in the world. We are developing an superconducting earthquake early detector using magnetic levitated test masses, differential frequency of which is 0.1Hz and the expected differential acceleration sensitivity is 3×10-14 m s-2 Hz-1/2. Besides detecting earthquake, we are designing an experiment to measure the gravity constant G as precise as 10ppm using the detector. In the future, we will try to demonstrate the key technologies of the new gravitational wave detector, SOGRO, such as low frequency and high quality factor magnetic levitation and so on.