Enacted by Prime Minister Yang Yan, the Double-tax Law was promulgated in 780 when De-zong, an emperor of the Tang Dynasty, came into throne; thereafter it had been in operation for 800 years.

两税法是唐德宗时宰相杨炎制定的，于建中元年(公元780年)颁布，此后在中国历史上一直沿用了八百年之久。