Two-dimensional (2-D) Golay complementary array sets (GCASs) have found important applications in massive multiple-input multiple-output (MIMO) systems equipped with a uniform rectangular array (URA), which are employed as precoding matrices to produce omnidirectional transmission. In this letter, new constructions of 2-D GCASs based on 2-D multivariable functions are presented. Compared with the existing constructions in the literature, the proposed constructions can be represented by explicit function forms that are more convenient to use in practical applications. Furthermore, 2-D GCASs with new parameters are obtained. Finally, numerical results show that the proposed 2-D GCASs are useful in massive MIMO systems.