In an omnidirectional wireless power transfer (OWPT) system, the frequent movement of load coils leads to a significant decrease in transmission power and efficiency. In order to obtain better-received power, the maximum power point tracking (MPPT) method for the load coil is commonly used. However, the existing methods are slow in detection speed and cannot achieve fast tracking effect on load movement. Based on the current amplitude modulation strategy, the mathematical model of the OWPT system with three orthogonal transmitting coils and one load coil is established in this article. By analyzing the relationship between load power and transmission power, the MPPT problem of the load coil can be transformed into an optimization problem of the maximum output power on the transmission coil side. And an invasive weed optimization algorithm is proposed to change the current injected into the orthogonal transmission coils to indirectly achieve the maximum power of the load coil. The experimental results demonstrate that the proposed algorithm reduces the convergence time of MPPT to less than 100 ms, and proves the correctness and feasibility of the method.