The disclosure provides a power allocation method for non-orthogonal multiple access (NOMA) systems and a base station thereof. The method is adapted to the base station and includes the following steps: receiving a first channel estimation error parameter from first user equipment, and receiving a second channel estimation error parameter from second user equipment; configuring a first minimum rate requirement of the first user equipment and a second minimum rate requirement of the second user equipment; determining a power allocation factor according to the first channel estimation error parameter, the second channel estimation error parameter, the first minimum rate requirement, and the second minimum rate requirement; and determining first transmission power for the first user equipment and second transmission power for the second user equipment according to the power allocation factor. |