According to the World Oral Health Report 2003, dental caries remains a major public health problem in most countries. Early detection is very important to the diagnosis and treatment of caries. The traditional dental caries detection methods, such as visual examination, probes, X-ray and other detection methods with low sensitivity and strong subjectivity, cannot meet the requirements of detecting early caries with high accuracy, reliability and specificity. Therefore, it is of great significance to find a kind of non-destructive, non-contact, high sensitive and high specific method to detect early caries. thermophotonic lock-in imaging (TPLI) detection technology based on photothermal effect is a non-destructive detection technology, and TPLI has the merit of high detection efficiency, large detection area and understandable detection result.Therefore, in this paper, artificially created demineralized on enamel of dental tissue was detected by TPLI, the detection ability of TPLI for caries regions which were selected on smooth surface, adjacent surface and the occlusal surface was investigated. The experimental samples were five molar teeth that had health surfaces and no visible defects, stains, or cracks. Two of them were spliced adjacently by epoxy glue to simulate adjacent surface. All samples were created 5 mm×5 mm rectangular windows on the smooth respectively , adjacent and occlusal surface, other surfaces were coated by acid-proof nail polish. Furthermore, the samples that artificially created demineralized on three different surfaces were imaged by TPLI and X-ray radiography after demineralized two days in the lactic acid gel (pH=4.5). The results showed that the amplitude value of caries area was larger than that of healthy area the phase delay became bigger due to demineralization. The amplitude images and phase images of TPLI were more sensitivity and more specificity to the artificial demineralization than the X-ray radiography. The smooth surface of a sample was selected to demineralize for different days, 1, 2, 4 and 6 d. Then the sample was imaged with TPLI and a X-ray radiography to decide quantitatively the degree of demineralization to prove the detection ability of TPLI. The results showed that the difference value of amplitude (healthy area amplitude and caries area amplitude) was 3.82 and the difference value of phase was 10.57° after 1d demineralization. However, X-ray detection method cannot recognize caries within demineralized 6d. The amplitude images and phase images of TPLI were consistent changes with caries time, and can found the caries very early. This paper proves the significance of TPLI to diagnosis and treatment of teeth.