According to massive data from core experiments，we systematically studied the main controlling factors of the clastic reservoir property difference in the Lower Member of the Lower Ganchaigou Formation within the same sedimentary system but different plays in the western Qaidam Basin. The results reveal that the variations in sedimentary environment，lithological characteristics，sand body thickness，burial history，geothermal gradients and lake water paleosalinity contribute heavily to the reservoir property difference. The distributary channel sand in the delta plain，the underwater distributary channel sand at the delta front and the beach-bar sand in the shore-shallow lake facies are widely developed in the Lower Member of the Lower Ganchaigou Formation of the western Qaidam Basin，providing a basis for high-quality reservoirs.Sand body thickness，matrix content and clastic particle are the important controlling factors of reservoir properties. Diagenesis plays a decisive role in reservoir evolution and properties，among which compaction has the strongest impact on reservoir properties，while cementation is a significant controlling factor in the local play. In the same sedimentary system，the difference in reservoir compaction strength is dominated by clastic particle sorting and matrix content of the distributary channel sand in the delta plain. Moreover，the variation in reservoir cementation strength is controlled by the particle size and thickness of both the distributary channel sand at the delta front and the beach-bar sand in the shore-shallow lake facies. In different plays，different burial history and geothermal gradients result in the great variation in reservoir compaction，while the circular and banded distribution of lake water paleosalinity around the salt lake center lead to the reservoir cementation difference on the plane.