Abstract: In order to determine the suitable harvesting period of southern type of poplar in Siyang area, at the same site conditions, the author took 3 m×4 m, 4 m×6 m, 6 m×8 m 3 different density planting, through 12 years of continuous biomass and afforestation cost accounting, analyzed the best input-output than, in order to obtain the maximum economic benefit as the harvesting period basis. The results showed that: the optimum harvesting period of the southern type of poplar planting density 208-833 plant/hm2 was 12-13 years.