In clinical diagnosis of cancer, immunology assay with single tumor marker often lead to a false and missed inspection. A quantitative method with a high degree of accuracy, sensitivity, and effectiveness is required for its diagnosis. We developed a dual-label time-resolved fluoroimmunoassay (TRFIA) to simultaneously detect carbohydrate antigen 125 (CA125) and carcinoembryonic antigen (CEA) in human serum to aid the diagnosis and prognosis of gastric cancer. The method was based on a microplate sandwich immunoassay using europium-labeled anti-CA125 antibodies and samarium-labeled anti-CEA antibodies as fluorescent reporters. The assay detection range was widely, and the limit of detection was sufficiently for detecting clinical sample. The intra- and inter-assay coefficients of variation were below 6%, and recoveries ranged from 90% to 110%. No significant statistical difference in sensitivity or specificity was observed between dual label-TRFIA and commercial chemiluminescent immunoassays in serum samples. These results demonstrate the successful development of an effective, reliable, and convenient novel TRFIA method for the simultaneous detection of CA125 and CEA, which can be used for clinical blood screening to monitor the occurrence and development of tumors to facilitate early treatment.