A resource indication method and apparatus and a communication system. The method includes: determining indication information, the indication information is used to indicate a second uplink resource in a second uplink frequency resource segment; wherein, the second uplink frequency resource segment or the second downlink frequency resource segment includes a second downlink predetermined number of second downlink resource block groups; and transmitting the first indication information to the UE in a first downlink frequency resource segment; wherein, the first downlink frequency resource segment or the first uplink frequency resource segment to which the first downlink frequency resource segment corresponds includes a first predetermined number of first uplink resource block groups, the first predetermined number being unequal to the second predetermined number; and wherein, the first indication information is bitmap information, a bit number of the bitmap information is determined according to the first predetermined number.