Let be a variable exponent function satisfying the globally log-Hölder continuous condition and L a non-negative self-adjoint operator on L2(Rn) whose heat kernels satisfying the Gaussian upper bound estimates. Let 421145cc8602f71f1aaa935611d"> be the variable exponent Hardy space defined via the Lusin area function associated with the heat kernels {e−t2L}t∈(0,∞). In this article, the authors first establish the atomic characterization of 421145cc8602f71f1aaa935611d">; using this, the authors then obtain its non-tangential maximal function characterization which, when p(⋅) is a constant in (0,1], coincides with a recent result by L. Song and L. Yan (2016) and further induces the radial maximal function characterization of 421145cc8602f71f1aaa935611d"> under an additional assumption that the heat kernels of L have the Hölder regularity.