A two-photon fluorescence labelling probe LP was synthesized and characterized, and LP-Ag was obtained by LP labelling N-protein antigen (Ag) of SARS-COV-2, and LP-Ag was made into an immunochromatographic test strip (TPICS)/ kit (TPICK). Clinical applications showed that, in comparison with the nucleic acid method (PCR)/ the colloidal gold method, of TPICS positive coincidence rate (PR), negative coincidence rate (NR) and total coincidence rate (TR) were 98.73 % / 98.26 %, 98.76 % / 99.20 % and 98.75 % / 98.75 %, and the consistency coefficient kappa value (K) was 0.972 / 0.975, and sensitivity (SE), specificity (SP) and accuracy (AC) were 98.99 % / 98.10 %, 99.55 % / 99.53 % and 99.38 % / 99.06 %, respectively. Detection results of Detection reagent and reference reagents were consistent (K > 0.75) with no statistical difference. Dilute blood sample used for testing is generally 25~50 μL (Whole blood sample 5~10 μL), and the test period is within 10 min. It not only avoids the disadvantages of cumbersome nucleic acid operation and long detection period, but also overcomes the instability of colloidal gold due to the shedding of the adsorbed functional groups, and has good application value. LP-Ag can be used for SARS-COV-2 imaging in cells to identify negative and positive.