A retransmission chipless tag with multiple U-shaped slot resonators is proposed to cut down the cost of traditional tags with chips. Multiple side-by-side U-shaped slot structures of different lengths are printed on the microstrip line, and the two terminals of the microstrip line are connected correspondingly with two orthogonal ultra-wideband (UWB) transceiver antennas to form the retransmission chipless tag. The U-shaped slot resonator has high Q values and narrow impedance bandwidth. The bandwidth that each resonator adds to the protection bandwidth is 300 MHz. Several 6-bit coding U-shaped slot resonator chipless tags are designed and fabricated for comparison and measurement. Results show that the simulation and the measurement are in agreement. The slot width of the U-shaped slot resonator and the distance between the resonators are reduced, resulting in deepened spectrum notch depth of the resonator. Decreasing the dielectric constant of the substrate or increasing the thickness of the substrate increases the spectrum notch depth of the resonator.