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<jats:title>Abstract</jats:title> <jats:p>We analyze the X-ray, optical, and mid-infrared data of a “changing-look” Seyfert galaxy SDSS J155258+273728 at <jats:italic>z</jats:italic> ≃ 0.086. Over a period of one decade (2009–2018), its broad H<jats:italic>α</jats:italic> line intensity increased by a factor of ∼4. Meanwhile, the X-ray emission in 2014 as observed by <jats:italic>Chandra</jats:italic> was about five times brighter than that in 2010 by <jats:italic>Suzaku</jats:italic>, and the corresponding emissions in the <jats:italic>V</jats:italic>-band, mid-infrared <jats:italic>W</jats:italic>1 band brighten by ∼0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e., <jats:inline-formula> <jats:tex-math> <?CDATA ${N}_{{\rm{H}}}\sim {10}^{21}\ {\mathrm{cm}}^{-2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>21</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em" /> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab7306ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, but the X-ray spectrum becomes harder in the 2014 <jats:italic>Chandra</jats:italic> bright state (i.e., photon index <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Gamma }}={1.52}_{-0.06}^{+0.06}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.52</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab7306ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) than that of the 2010 <jats:italic>Suzaku</jats:italic> low state (<jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Gamma }}={2.03}_{-0.21}^{+0.22}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.21</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.22</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab7306ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>). With an Eddington ratio being lower than a few percent, the inner region of the accretion disk in SDSS J155258+273728 is likely a hot accretion flow. We then compile from literature the X-ray data of “changing-look” active galactic nuclei (AGNs), and find that they generally follow the well-established “<jats:italic>V</jats:italic>”-shaped correlation in AGNs, that is, above a critical turnover luminosity the X-ray spectra soften with the increasing luminosity, and below that luminosity the trend is reversed in the way of “harder when brighter.” This presents direct evidence that CL-AGNs have distinctive changes in not only the optical spectral type, but also the X-ray spectral shape. The similarity in the X-ray spectral evolution between CL-AGNs and black hole X-ray binaries indicates that the observed CL-AGNs phenomena may relate to the state transition in accretion physics.</jats:p>