In order to obtain transmission property of tunneling rays in a short length large-core SI-PDF fiber, a formula is derived by a light-ray projection integral method to calculate the power coupled from laser beam with different incident angles in the SI-PDF fiber. The output power characteristics of laser beams of 3,67,140 m length fibers at different incident angles are achieved respectively by measurements and theoretic calculations. The loss coefficiens are obtained by the least square fitting to experimental data at a logarithm coordinate. Results show that the coupled power and the loss coefficients with different incident angles in the SI-PDF fiber keep almost a constant at 0~12°,and the coupled power goes down exponentially with different incident angles beyond 12°.Moreover,the loss coefficients increase with increase of incident angles,it is 26 dB/km at 12° and 82 dB/km at 28°。