The Target Echo Signal Simulator (TESS) for interferometric SAR was designed and implemented. The TESS can make a hardware-in-loop simulation loop with radar working in interferometric bistatic mode. It recorded the transmitting signal of the master satellite in real-time, supplemented the scene modulation information off-line, and played back the radar echo of master and slave satellite according to the radar PRF. The high digital IF transmitting and receiving technique was used to achieve better harmonic, clutter and carrier suppression performance. The on-line loop correction technique was adopted to correct the amplitude and phase mismatch of TESS in real-time. The measured results show that the indexes of TESS satisfy the design requirements, and the TESS meets the needs of practical engineering of the hardware-in-loop simulation for interferometric SAR.