Objective: To investigate routine blood test results and secular changes among Tibetan children and adolescents aged from 3 to 19 in the plateau, and to provide the basis for reference range of routine blood test for this population. Methods: A total of 1 568 Tibetan children and adolescents aged from 3 to 19 living in Shigatse, Tibet were selected by cluster random sampling method. Routine blood test results and its secular trends were compared by age and gender. Results: Significantly differences were found in red blood cell(RBC), hemoglobin(HGB), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin(MCH), white blood cell(WBC), neutrophil(NEU), neutrophil percentage (NEU%), lymphocyte(LYM), lymphocyte percentage(LYM%)，monocyte percentage(MON%)，eosinophil percentage(EOS%),basophil percentage(BAS%) and platelet(PLT) among the four age groups of 3-5, 6-12, 13-15, and 16-19 years ( F/H =60.22, 179.41, 249.45, 115.03, 74.90, 14.33 , 33.46, 78.90, 49.20, 97.29, 24.45,24.28,42.65,20.10, P <0.05). Among red blood cell indexes, RBC, HGB, HCT,MCH increased with age in boys( F =148.77, 493.04, 623.14, 249.92, P <0.05), but there was no similar trend in girls( F =1.37, 0.15, 2.94, 0.11, P >0.05). HCT showed significant sex differences among the four age groups of 3-5 years, 6-12 years, 13-15 years, and 16-19 years [(41.33±2.31)% vs (41.98±2.40)%; (43.28±2.60)% vs ( 43.75 ±2.36)%; (46.20±3.11)% vs (44.83±2.67)%; (51.10±4.15)% vs (43.61±4.70)%, t =-2.10, -2.88, 3.50, 10.82, P <0.05]. WBC, NEU, NEU%, LYM, LYM%, monocyte(MON), and MON% increased significantly with age in both boys and girls ( P <0.05). From the age of 12 to 13, RBC, HGB and HCT in Tibetan male and female adolescents showed an opposite trend and widened gradually. Conclusion Red blood cell index shows significantly different trends among Tibetan adolescents and children of different ages and genders. Regional nationality, age, gender, and other factors should be considered when developing the reference value range of blood routine index.