This paper describes a ΔΣ modulation based ranging method for the IR-UWB radar system. To relax the phase resolution requirement of the delay line in the receiver, two coarse timing boundaries of the delay line are used to form a bi-level quantizer which can be the part of a 1-bit ΔΣ oversampling TDC. Also, a digital phase-rotator circuit is designed to provide unlimited phase capture range. In the simulation, the proposed ΔΣ IR-UWB radar designed in 0.18mm CMOS can achieve the ranging resolution of 0.46mm.