The rainy season from June to September is the best time to visit Huangguoshu. Water volume is highest from July through August, when the falls run at full width and the Rhinoceros Pool below becomes a churning basin of white water. The spray from the base reaches far enough to keep the surrounding cliffs permanently damp and the vegetation lush.
Outside the rainy season, the falls narrow considerably. October through December is dry and clear — pleasant for walking but less spectacular for the falls themselves. Winter (January to March) sees the lowest water levels; the falls are still impressive but not the same scale. Spring brings increasing flow as rain returns, with May a reasonable compromise between crowds and water volume.
The site draws enormous visitor numbers during Chinese national holidays — Golden Week in early October and the May 1st break are genuinely overwhelming, with queues for the shuttle buses measured in hours. If your visit falls during these periods, arriving before 8am gives you a reasonable window before the worst of it.