Objective:To investigate the long-term effects of GnRHa treatment on final height gain, gonadal function, and body mass index(BMI) in children with central precocious puberty(CPP) or early and fast puberty(EFP), and to explore the influencing factors of height gain and early predictors.Methods:Fifty patients with CPP and 44 patients with EFP who were treated with GnRHa for more than 2 years were enrolled(80 females and 14 males). Body height, bone age, BMI, gonads hormone, uterus and ovarian volumes(female), testicular volume(male), and other parameters before and after treatment were measured.Results:(1)For girls: GnRHa plus GH treatment gained more final height compared with GnRHa treatment [(10.69±5.73) cm vs (7.42±5.76) cm, P<0.05]. Height lost >5cm at the initial treatment benefited much more for the final height compared with height lost<5cm [(10.65±3.32) cm vs (6.51±3.40) cm, P<0.01]. The proportion of overweight/obesity decreased when reaching the final height compared with the initial treatment and stopping the treatment. Serum LH level, uterine and ovarian volume were significantly decreased after stopping treatment compared with before treatment, and increased half a year to 1 year after stopping treatment.100% of girls had menarche and 95% reached the regular cycle 3 years after stopping treatment.(2)For boys: GnRHa plus GH treatment and GnRHa treatment gained height by(8.78±5.2) and(7.99±4.82) cm, respectively. Serum LH level and testicular volume were significantly decreased after stopping treatment as compared with those before treatment, and increased for half a year to 1 year after stopping treatment. Conclusion:GnRHa treatment can significantly improve the final height for girls with CPP and EFP. The patients with more height lost could gain more height, which can be used as a predictor of height gain.