Plug seedlings are increasingly used in vegetable cultivation in Japan, because they are suitable for machine operations and are disease resistant; however, in cabbage cultivation, variation in seedling growth affects plant growth after transplanting to the field, and eventually, harvesting all the cabbages at the same time is not possible. In this paper, a simulation model used to express the growth variation in cabbage plug seedlings is proposed to reveal their cultivation characteristics and consider a cultivation technique that would produce uniform growth among seedlings. In this simulation model, the mutual shading among neighbouring plug seedlings resulting from high-density planting, which is one of the factors of variation in seedling growth, was modelled. The model parameters were obtained from the results of a cultivation experiment comparing growth against the light quantity that seedlings could receive; however, there were differences between the growth of a single seedling in the cultivation experiment and the growth of the plug seedlings. It is believed that growth rate and mass would be greater for a single seedling than for the plug seedlings. This simulation was able to express the growth variation of the actual plug seedlings by adjusting the model parameters.