Due　to　its　excellent　mechanical　properties,　15CrMo　steel　is　widely　used　in　critical　components　exposed　for　high-temperature　and　high-pressure　conditions.　Long　term　high-temperature　will　increase　the　spheroidization　possibility　and　even　cause　serious　safety　accidents.　However,　characterization　of　the　spheroidization　grades　is　a　very　difficult　problem.　To　quantitatively　evaluate　the　spheroidization　grades　of　15CrMo　steel,　destructive　testing　methods　are　used　to　determine　spheroidization　grades.　This　study　uses　the　ultrasonic　backscattering　method　to　detect　the　spheroidization　grades.　The　ultrasonic　testing　platform　collects　the　backscattering　signals,　and　the　typical　characteristic　parameters　and　entropy　characteristic　parameters　of　the　backscattering　signals　are　extracted.　New　entropy　characteristic　parameters,　including　the　information　entropy,　conditional　entropy,　sample　entropy,　fuzzy　entropy,　permutation　entropy,　approximate　entropy,　power　spectral　entropy,　and　singular　spectrum　entropy,　are　introduced　to　evaluate　the　spheroidization　grades　of　15CrMo　steel.　It　is　found　that　the　proposed　entropy　characteristic　parameters　can　reflect　the　changes　in　the　microstructure　under　different　spheroidization　grades.　Therefore,　the　entropy　characteristic　parameters　of　ultrasonic　backscattering　signals　are　advantageous　for　evaluating　the　spheroidization　grades　of　15CrMo　steel.　©　2025　Elsevier　Ltd