In this paper, dynamical LMS algorithm and global optimization algorithm, with a view to gradient of error probability, are proposed based on analysis of sub-carries allocation space for OFDM system. Global optimization algorithm comes from combined GA. Relative to Hughes-Hartogs algorithm, these two algorithms are lower in complexity, and they both have recurrence characteristic. Simulation result shows that dynamical LMS algorithm is close to the optimum in fast fading channel, and the combination of dynamical LMS algorithm and global optimization is close to the optimum in slow fading channel in efficiency.