In this paper we propose a two-pole varactor-tuned superconducting filter using coplanar waveguide (CPW) spiralin-spiral-out (SISO) resonators.Novel inteal and exteal coupling structures are introduced to meet the requirements for a tunable filter with a constant absolute bandwidth.The fabricated device has a frequency tuning range of 14.4％ at frequencies ranging from 274.1 MHz to 317.7 MHz,a 3-dB bandwidth of 5.14 + 0.06 MHz,and an insertion loss of 0.08 dB-0.70 dB.The simulated and measured results are in excellent agreement with each other.