Abstract: We examined the effects of retention density on plant DBH (diameter at breast height), height, volume growth, stand biomass, and stand economic benefit of Cunninghamia lanceolata plantation by Pingxiang, Guangxi Province. Four treatments of different retention density were set up a 14-year middle-aged Cunninghamia lanceolata plantation, 500, 750 and 1000 trees·hm^-2, with stand without thinning as the control (1500 trees·hm^-2). Results showed that DBH (20.55 cm), increment in height (15.70 m), and large-diameter timber volume (18.31 m³·hm^-2) of the C. lanceolata plantation were the highest in 500 trees·hm^-2 treatment. The volume of living trees was the highest in the control (199.63 m³·hm^-2), which was significantly higher than that in 500 and 750 trees·hm^-2. The biomass of arbor layer and ecosystem, as well as the economic benefit differed significantly across the treatments, with arborous biomass (90.72 t·hm^-2), ecosystem biomass (94.97 t·hm^-2), and economic benefit (1.184×10⁵ yuan·hm^-2) of 1000 trees·hm^-2 treatment being significantly higher than others. Reducing stand retention density increased the DBH, plant height, timber diameter, proportion of large diameter timber, average volume and biomass of single timber, but it did not enhance the volume of living trees. The retention density of 1000 trees·hm^-2 was the optimum for middle-aged C. lanceolata plantation. Compared with the control, it significantly increased the total stand volume, arbor biomass, ecosystem biomass, and economic benefit by 2.3%, 5.7%, 4.7%, and 5.8%, respectively.