A reliable and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed in this study for clinical testing of 24-h urinary fractionated metanephrines (MNs) and 3-methoxytyramine. At first, the acid hydrolysis condition was well optimized. Following solid-phase extraction (SPE) was performed to purify urine specimens, and the obtained elutes were directly used for LC-MS/MS analysis. A total run time of 3 min for each sample made it possible to analyze more than 300 samples per day. This method was validated with good linearity (linear correlation coefficient >= 0.9969), favorable precision (the coefficients of variation <= 10.2%), satisfactory recovery (85.0%-108%) and negligible matrix effect (92.0%-109%). The reference intervals of these analytes in Chinese subjects were established for clinical application in diagnosis of pheochromocytoma. This reliable and well-validated measurement method for 24-h urinary fractionated MNs and 3-methoxytyramine using LC-MS/MS could be successful used in clinical testing for diagnosis of pheochromocytoma.