From the group statistical theory, and with a pseudochemical reaction mechanism, a new universal equation is proposed to calculate the dielectric constant for binary solutions. The simple form of the new model makes it convenient to use and all its parameters have obvious physical meanings. With this model, we explained the experimental phenomena and empirical rules in cited works. Tested by 225 kinds of binary systems, the overall average relative deviation at 4228 data sets is 0.775 % and the results show that this new model is more accurate than the cited models. This model is especially suitable for associative and asymmetric systems.