At an extremely low temperature of 20 inK, we measured the loop current in a tunable rf superconducting quantum interference device （SQUID） with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop （Фf） and the small dc-SQUID （Фfcjj）, respectively, the potential shape of the system can be fully controlled in situ. Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.
