At present, limited data exists to discuss the characteristics of suprasellar arachnoid cysts (SACs). The aim of this study is to elucidate the relationship between characteristics of cysts and outcomes, quantitatively analyze improvement in hydrocephalus, and evaluate the risk factors for the prognosis of SACs treated by endoscope. From June 2002 to 2017 December, 247 cases of SACs treated by endoscope in Beijing Tiantan Hospital were included in this study. The severity of hydrocephalus was evaluated by Evans’ index (EI). The results showed that the slit-valve and the transparent/thin membrane were noted in 86.2% and 76.5% of overall patients, respectively, and the distribution differences among age-groups were statistically significant (p < 0.01). After a mean follow-up duration of 73.1 months, 18 patients underwent a reoperation. Ventriculocystostomy (VC) (hazard ratio (HR), 3.37; 95% confidence interval (CI), 1.2–9.47; p = 0.024) and history of treatment (HR, 3.98; 95% CI, 1.31–12.31; p = 0.015) were adverse factors for reoperation rate. MRI at 1-year follow-up revealed mean decreases of 78.4% and 9.13% in cyst size and EI. No paraventricular edema was an adverse factor associated with the improvement in hydrocephalus (HR, 11.22; 95% CI, 5.43–23.18; p < 0.01). These results indicated that ventriculocystocisternostomy (VCC) and no history of treatment is favorable factors for prognosis of SACs treated by endoscope. If feasible, VCC is the optimal choice for SACs. Slit-valve phenomenon and transparent/thin membrane are correlated with age but did not influence the outcomes of endoscopic fenestration. The mechanism for the expansion of cysts may be different between child and adult patients. Paraventricular edema is a favorable factor for the improvement in hydrocephalus after endoscopic surgery.