Ambient backscatter is a new green tech-nology for Internet of Things (IoT) that utilizes sur-rounding wireless signals to enable batteryless devices to communicate with other devices.The battery-free devices first harvest energy from ambient wireless sig-nals and then backscatter the signals for communica-tions.Clearly,sensitivity and distance are two im-portant parameters for system performance.However,most existing studies on ambient backscatter commu-nication systems do not consider the impact of the sensitivity of the energy-harvesting nodes and the dis-tances between these devices.In this paper,we first provide a literature review for ambient communica-tion technology and then take sensitivity and distance as two key parameters and investigate the sensitivity and distance based performance for ambient backscat-ter communication systems.Specifically,we estab-lish the mathematical model based on distances be-tween transceivers and backscattering nodes,extract a parameter that can differentiate the direct path and the backscattering path,evaluate the effects of trans-mit beamforming,design an energy detector for the reader,and analyze the outage probability of energy harvesting at the tag and the bit error rate (BER) at the reader.Simulations are then provided to corroborate the proposed studies.