The present invention discloses a method for solving non-controllability of terminal's power spectrum density in OFDMA system. It considers the problem of non-controllability of terminal's carrier transmit power resulting from the indeterminacy of carrier number allocation to the terminal in the OFDMA system which is solved by introducing the maximum carrier number that can be allocated to the terminal by combing AMC, the power control and the dispatching. By applying the present invention, the carrier power of the terminal can be best controlled by the system, it is most possible for the terminal to transmit power on carrier completely according to a set value, while it is greatly reduced the possibility that the terminal's power spectrum density is suddenly decreased out of control, which is caused by the summation of carrier powers in the set value exceeding the maximum total transmit power. Moreover, it is avoided occurrence of a large amount of error codes in that condition and the waste of power resources resulting from the excessive restriction on the carrier power.