To enhance the quality of commercial fruits, it is imperative to detect mechanical damage at an early stage. Aiming to addresse the issue of unclear spectral evolution mechanisms in the early stages of fruit damage, leading to low accuracy and robustness of the damage detection model. The temperature difference time series data of damaged and undamaged areas in the early stages (0~2h) of mechanical damage was collected to Red delicious apples, and combined it with the spectral features of sensitive bands (1255~1314nm) by using the Granger causality test method to reveal and substantiate the mechanism of spectral feature evolution caused by temperature changes: with the progression of apple damage, the temperature difference was firstly risen, then fell, and finally stabilized. The more severe the damage was, the greater the temperature difference would be. The results of the Granger causality test indicated that the main cause of the change in the spectral features of the apple’s damage site in the 1255~1314nm characteristic band was the change in temperature at the site of damage. The milder the damage was, the weaker the influence of the temperature difference on the spectral features would be. The spectral features R were more representative and comprehensive in characterizing the surface temperature of the apple after damage. Through the study of the evolution mechanism of spectral features after the Red delicious apples was bruised, the research result can provide a theoretical basis and research approach for more reliable early detection of minor apple damage.