Pre-mRNA splicing is a key process in the gene expression of eukaryotic cells, which includes two major procedures: the cutting of introns and the union of exons. This paper proposes a algorithm to simulate the Pre-mRNA splicing process in the Analog-Cell, which was developed independently. Using the algorithm, the correct results are consistent with the biological principles. Through simulation of the process, the study has found that this algorithm has the capacity to make the introns to form the lariat structure efficiently and accurately, meanwhile to unit the exons selectively. In this way, the Analog-Cell can finish the formation of the mature mRNA.