In this work, we develop a novel robust scheme of two-dimensional unequal error protection (2D-UEP) for the H.264 scalable video coding (H.264/SVC) with a combined temporal and quality (SNR) scalability over packet-lossy networks. The proposed scheme combines error resilience techniques and importance measures in video coding. To avoid the waste of bits and obtain the best rate allocation, we develop a threshold-based UEP (TH-UEP) algorithm. The TH-UEP designs a predefined threshold according to the length of packet and the error correcting ability of RS code to achieve the best allocation. In addition, the proposed scheme also derives a simple mathematical model to reduce computational load of the best rate allocation. Experimental results demonstrate that the proposed H.264/SVC video transmission scheme using UEP can provide strong robustness and video quality improvement when compared to other 2-D UEP schemes.