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Crack closure may be a major factor in causing differences between growth of small and large cracks.The purpose of the present paper is to use an analytical model of crack closure to study the crack closure behavior of the small crack emanating from a semi-circular notch under tension loading (SENT).Results indicate that small crack in notched member exhibit lower crack opening stress than longer cracks, and the crack opening stress change with increasing crack length.Small-crack effects are more pronounced at lower stress ratio and higher stress level.According to the above calculation results, a crack opening stress equation which considers the influence of the crack length is given.It is anticipated that the proposed crack opening stress equation for SENT specimen will eventually improve prediction capability for fatigue crack growth rates and fatigue crack growth lives.