The present disclosure provides a method and a device in a base station used for Unlicensed Spectrum. The base station first transmits K1 radio signals in a reference time window and then receives K1 HARQ feedbacks, and performs Q1 energy detections respectively in Q1 time sub-pools on a first frequency sub-band; the K1 HARQ feedbacks are respectively used for determining whether the K1 radio signals are correctly received; a first radio signal is a radio signal of the K1 radio signals, the first radio signal carries part of bits comprised by a first bit block; a first HARQ feedback is used for determining whether the first radio signal is correctly received, HARQ feedback(s) other than the first HARQ feedback among the K1 HARQ feedbacks is(are) used for determining the Q1 time sub-pools. The present disclosure increases the chance of access to Unlicensed Spectrum and the utilization ratio of spectrum resources.