In this paper, the particle-in-cell/Monte Carlo method simulation algorithm with independent intellectual property is described in-depth. The discharge properties of the J-PARC multicusp ion source are investigated using this algorithm. The discharge mechanism of the J-PARC ion source is discussed, and the ion source volume production efficiency is analyzed under single correction magnet and double correction magnets. The results show that under the single correction magnet, a maximum volume production efficiency can be obtained when the distance between the center of the correction magnet and the top of the ion source is 50 mm; fixed the top one of double correction magnet, the longer the distance between magnets, the lower the volume production efficiency is.