A simply and analytical formula of the axial light intensity distribution behind a circular aperture is derived by using the helmhotz - kirchhoff integral theorem and the kirchhoff ' s boundary conditions . it is studied the nonparaxial on - axis intensity distribution throughout the whole space behind a circular aperture . an accurate formula to calculate the fresnel number of circular aperture is presented and the validity of usual fresnel number formula is reexamined . by using the analytical formula and diffraction integral formula , some numerical simulation comparisons are done , and it is shown that the results of the two methods are completely coincident 用亥姆霍茲-基爾霍夫積分定理和基爾霍夫邊界條件,推導出了平面波經(jīng)小圓孔非傍軸衍射時軸上強度的簡單解析表達式,研究了平面波經(jīng)小圓孔后整個衍射空間非傍軸的軸上光強分布.給出了計算圓孔菲涅爾數(shù)的精確公式,重新檢查了通常的菲涅爾數(shù)公式的有效性.數(shù)值計算顯示,應用解析表達式所得的結(jié)果與應用衍射積分公式所得的結(jié)果完全一致