A novel optical element - step refractive index combined triangular-section prism generating non-diffracting linear structured beam with longer distance is proposed. This element is designed with gluing positive and negative isosceles triangular-section prisms. Its property is the same as single positive isosceles triangular-section prism for beam transformation, and its equivalent index of refraction is decided by the difference of refraction index of positive and negative isosceles triangular-section prisms. Therefore, we can get an equivalent index of refraction closer to 1 by combining positive and negative isosceles triangular-section prisms with the approximate index of refraction. And also the non-diffracting linear structured beam with longer distance can be obtained. The technical problem of difficulty in machining the small bottom corner is solved. The formation mechanism of the non-diffracting linear structured beam is analyzed by geometrical optics, and the relevant parameters are also calculated. The intensity distribution is simulated by diffraction and interference theory. The results show that when a plane wave illuminates on the novel optical element, a non-diffracting linear structured beam is formed in longer distance.