The research aims to study the effect of 5-10-15 training on developing anaerobic speed reserve, some physical and physiological variables and the time-trial level of 800-m running race for juniors under 18 years, The researchers use experimental methodology with two groups design (experimental and control) and with pre-post measurements, The research sample was chosen in Purposive method, (10) 800-m running juniors were divided as follows (5) juniors for the experimental group, (5) juniors for the control group, The researchers add 5-10-15 training program (8 weeks by three training units per week), the results of this study 5-10-15 training has a positive effect on developing anaerobic speed reserve, some physical (sprint - muscular power - speed endurance) and physiological (Maximal aerobic speed - Vo2max - maximal anaerobic power - fatigue index) variables and the time-trial level of 800-m running race for juniors under 18 years, The researchers recommend to use 5-10-15 training on developing anaerobic speed reserve, some physical and physiological variables and the time-trial level of running races, In addition to directing the results of this study to track and field coaches to be able to benefit from its results.