Genotype imputation has become an indispensable part of genomic data analysis.  In recent years, imputation based on a multi-breed reference population has received more attention, but the relevant studies are scarce in pigs.  In this study, we used the Illumina PorcineSNP50 Bead Chip to investigate the variations of imputation accuracy with various influencing factors and compared the imputation performance of four commonly used imputation software programs.  The results indicated that imputation accuracy increased as either the validation population marker density, reference population sample size, or minor allele frequency (MAF) increased.  However, the imputation accuracy would have a certain extent of decrease when the pig reference population was a mixed group of multiple breeds or lines.  Considering both imputation accuracy and running time, Beagle 4.1 and FImpute are excellent choices among the four software packages tested.  This work visually presents the impacts of these influencing factors on imputation and provides a reference for formulating reasonable imputation strategies in actual pig breeding.