Based on the negative eigenvalue theory we discuss the non-diagonal disorder and dimensional effects for the electronic structure in low-dimensional disordered systems. The result shows that: It is the non-diagonal disorder and the dimensio nal effect that strongly affects the electronic structure in the low-dimensional disordered system. The non-diagonal disordered mainly shows the changes of the structure and the boundary effects of the particles in the system. From one- dim ensional system to narrow gap one, the number of the electronic bandgap decrease s, the degree of local states increases, and the structure of the energy gap wil l be more complicated.