本文以太阳日冕软X射线Fe XVII光谱线中1.501 nm谱线为例，分析了不透明度对1.501 nm谱线的影响，再讨论了太阳日冕等离子体温度和电子数密度的诊断原理。结果表明，太阳日冕等离子体温度的数量级为10⁶K ，电子数密度的数量级为10¹⁰cm^-3，这些都和实际观测数量级完全相同。通过分析，得到了一些重要结论。本研究对太阳日冕等离子体诊断具有重要的参考意义和价值。<br/>In this paper, taking the 1.501 nm spectral line in Fe XVII spectral lines in solar coronal soft X-ray as an example, we analyze the effect of opacity on the 1.501 nm spectral line, then we discuss the diagnostic principle of plasma temperature and electron density. Results show that, the plasma temperature in solar coronal has the 10⁶K order of magnitude, and the electron density has the 10¹⁰cm^-3 order of magnitude, which has the same order of magnitude in actual observation. Through analysis, we obtain some important conclusions. This study will have reference significance and value in solar coronal plasma diagnostic.