Gene expression is essentially a random process. The distribution of expression product quantities can comprehensively describe the stochastic behavior. of gene expression, which typically exhibits three distribution shapes: decaying, bell-shaped, and bimodal. Ref. [21] explores a stochastic gene expression model of minimal coupled positive-plus-negative feedback loop. By constructing two continuous curves C1 and C2 in the parameter phase, the necessary and sufficient conditions for the model to generate three distribution shapes were theoretically provided. However, for any given set of parameters, since the curves C1 and C2 cannot give exact expressions, it is difficult to directly and quickly determine which distribution shape the stochastic gene expression model of a minimal coupled positive-plus-negative feedback loop can generate. This greatly affects our research on massive single cell transcriptomic data using mathematical models. In this paper, we present several system parameter conditions that generate the three distribution shapes by quantitatively characterizing the curves C1 and C2. These parameter conditions can be calculated using simple elementary functions. Thus, a rapid discrimination method for determining the distribution shape of the quantity of expression products in the stochastic gene expression model is provided.