Abstract： Shale samples in an open environment, on the one hand, experience significant loss of light hydrocarbons due to pressure release, and on the other hand, due to temperature reduction, the viscosity of retained hydrocarbons increases and their state changes, making it difficult to accurately quantify shale oil content under in-situ temperature and pressure conditions using nuclear magnetic resonance at room temperature. This study takes the Qingshankou Formation shale of the Cretaceous from the Songliao Basin as an example, typical shale samples in the low and high maturity stages were selected. Nuclear magnetic resonance detection were performed on high mature shale samples with different degrees of pulverization, as well as low and high mature shale samples under different temperature conditions, to quantify the fluid loss and state transformation during the pulverization and heating processes, and determine the oil content characteristics under the influence of temperature. The results showed that during the process of crushing shale from standard plunger to ~0.04 cm, the morphology of its T2 spectrum, the total signal amount of T1-T2 spectrum, and the signal amount of each hydrogen containing component remained basically unchanged. Therefore, prolonged exposure to shale samples during the crushing process will not result in significant residual fluid loss. As the temperature of shale samples increases, the light oil signal increases and the water signal decreases in low mature shale, while the oil and water signals decrease in high mature shale. At the same time, the signal of hydroxyl compounds in shale decreased, and its signal level was restored after returning to room temperature. It can be seen that as the temperature increases, free water continues to evaporate; The pre-oil bitumen of low mature shale with high viscosity at room temperature changes from a solid-like state to a liquid light oil. After 100 ℃, the absolute amount of NMR light oil increases by 107%; In high mature, the shale oil bitumen becomes light oil at room temperature, and heating will cause it to evaporate and dissipate. The decrease and increase of hydroxyl containing compounds with temperature rise and fall reflects the controlling effect of temperature on clay adsorption of water. Therefore, when using NMR to evaluate the oil content of low mature shale, attention should be paid to the transformation of the pre-oil bitumen under temperature conditions to avoid underestimating the shale oil content.