Grotto temples face extensive damage from natural factors and human activities and salt erosion is a critical issue. Quantifying the damage extent in surface salt efflorescence stage is crucial for subsequent preservation efforts. This study investigates salt efflorescence in the North Grotto Temple in Qingyang City, Gansu Province, employing PFC 2D software to simulate surface salt formation. Active thermal infrared detection is used to examine the relationship between temperature changes and efflorescence thickness. Results indicate that when subjected to identical stimuli, the temperature of sandstone surface is lower than that of saltated surfaces and surface temperature increases as salt efflorescence thickness increases. A power function fitting the normalized temperature-time curves reveales a notable negative linear relationship between the exponent and salt efflorescence thickness. This exponent can serve as a warming index, realizing the quantitative assessment of salt efflorescence damage.