Related are a method, an apparatus, user equipment and a base station for sending and receiving SI. The method of receiving SI comprises: in response to receiving first-class SI broadcast by a base station, determining a requesting window, a receiving window and a pilot code of to-be-requested SI, where the requesting window includes P number of time domain sending opportunities for sending a request carrying the pilot code; monitoring a first Q number of time domain sending opportunities within the requesting window to determine whether a request carrying the pilot code is sent from UE to the base station; when no UE sends the request carrying the pilot code, sending the request carrying the pilot code in the (Q+1)-th time domain sending opportunity; and monitoring the receiving window of the to-be-requested SI for the to-be-requested SI sent by the base station.