The present invention provides a method and apparatus for determining a transmission power of a secondary transmitter in a hierarchical spectrum sharing system. The method can comprise steps of obtaining channel quality information on a primary link from at least one primary receiver within a transmission range of the secondary transmitter; and determining the transmission power for the secondary transmitter based on the channel quality information, wherein the transmission power is matched with the channel quality indicated by the channel quality information. According to the embodiments of the present invention, a power control scheme is applied to the secondary transmitter based on the channel quality information on the primary link. In such a way, the secondary transmitter' throughput can be improved with controllable rate loss to the primary receiver and accordingly the spectrum efficiency for the whole system can be further upgraded.