Transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are the main pathogens causing viral diarrhea in pig, mixed infections of these two viruses are very common in intensive pig rearing. However, there is a lack of a method to simultaneously detect and distinguish PEDV and TGEV in preclinical levels. In this study, we aimed to establish a dual ultrasensitive nanoparticle DNA probe-based PCR assay (dual UNDP-PCR) based on functionalized magnetic bead enrichment and specific nano-technology amplification for simultaneous detection and distinguish diagnosis of PEDV and TGEV. The detection limit of dual UNDP-PCR for single or multiple infections of PEDV and TGEV is 25 copies/g, which is 400 times more sensitive than the currently known duplex RT-PCR, showing better specificity and sensitivity without cross-reaction with other viruses. For pre-clinical fecal samples, the dual UNDP-PCR showed a markedly higher positive detection rate (52.08%) than conventional duplex RT-PCR (13.21%), can rapidly and accurately identify targeted pathogens whenever simple virus infection or co-infection. In summary, this study provides a technique for detecting and distinguishing PEDV and TGEV in preclinical levels, which is high sensitivity, specificity, repeatability, low cost and broad application prospect.