Two current-model-based approaches are presented to accelerate the calculation of the magnetic field of permanent-magnet-array(PMA) that consists of magnet blocks. It enables a speedy convergence of optimization of a PMA design that is a key component of the popular body-part-dedicated portable MRI in the recent years. This method can be extended to magnet of other shapes. Both Halbach(60blocks) and sparse Inward-Outward ring-pair-PMA(1,200 blocks) are used as examples to demonstrate the speed and accuracy of the algorithm. The best acceleration is 78.92% and 77.94%calculation-time reduction compared to the conventional nested for-loops, and 99.81% and 99.91%reduction compared to FEM-based commercial software.