Although the fixed-step Perturbation and Observation Maximum Power Point Tracking (P&O MPPT) is a commonly applied algorithm for wave power generation, its tracking performance is weakened in irregular waves. To overcome the disadvantage, this paper proposes a novel 2-D lookup table based (2DLTB) MPPT scheme. It utilizes a 2-D optimal-duty-cycle table and real-time wave data to tune the duty cycle of pulse-width-modulation (PWM) signal. Two tuning methods are introduced. The first one is called single-wave-period regulation (SWPR), which adjusts the duty cycle wave by wave. The second one named multiple-wave-period regulation (MWPR) tunes the duty cycle at intervals of multiple wave periods. Both 2DLTB MPPT and the fixed-step P&O MPPT are simulated and compared in different irregular waves generated from the real sea states. Results show that 2DLTB MPPT is insensitive to the number of waves. However, the fixed-step P&O MPPT is sensitive to both update duration and step size. Meanwhile, 2DLTB MPPT has the stronger power tracking performance than the fixed-step P&O MPPT. In addition, SWPR outperforms MWPR in the short time window, while MWPR performs better in the long time window. In general, as a simple, reliable and excellent MPPT algorithm, 2DLTB MPPT is worthy of promotion.