In the era of the smart grid, the electrical load on the demand side becomes more dynamic and less predictable than ever before. Differently from deterministic load forecasting, probabilistic load forecasting (PLF) estimates the uncertainty of future loads and has become increasingly important for power system planning and operations. We have previously proposed a deterministic load forecasting method by improving the Informer model in which the periodic property of load profiles is considered. In this paper, a PLF model is designed on the basis of the deterministic load forecasting method. The PLF model estimates the model and data uncertainties through running the deterministic load forecasting model several times with random initial parameters, and determines load intervals by combining the average value of multi runs of the deterministic load forecasting model, the estimated uncertainties and the critical value of the standard normal distribution. The experimental results on GEFCom2014 data set have demonstrated the superior forecasting performance than others.