Abstract: This paper reviews the conventional SIF (Stress Intensity Factor) models for semi-elliptical surface cracks in welded joints, namely Newman-Raju-Maddox model and Yamada-Hirt-Albert model. The shortage of Yamada-Hirt-Albert model is pointed out, by which SIF in uniform tension cannot be calculated reasonably. After analysing current research data in the literature, new SIF formulae are developed which modifies Yamada-Hirt-Albert model. It is verified that the improved formulae are more reliable by comparison with Benchmark data and other experimental results published in several literatures.