Abstract: The present disclosure provides a method and device for communication on unlicensed spectrum in a UE and a base station. In view of PUCCH resource waste and transmission delay increase that are caused by configuring too much unlicensed spectrum, in the present disclosure, logical information is configured so that PDSCHs transmitted through different sub-frames on different physical carriers form one logical carrier, and an HARQ operation is performed on the logical carrier. As an embodiment, HARQ_ACK resources are reserved according to the number of logical carriers currently configured, and a system uses dynamic signaling to indicate an index of an HARQ_ACK corresponding to a scheduled PDSCH in the reserved HARQ_ACK resources. The solution provided in the present disclosure saves PUCCH resources and reduces the HARQ delay. Besides, the present disclosure reuses as much as possible the PUCCH resource allocation scheme and HARQ transmission scheme in the existing LTE, and has good compatibility.