[Objectives]  This research is to evaluate the effectiveness of Harmonia axyridis as a natural enemy for controlling Poratrioza sinica Yang & Li in the field. [Methods]  The population dynamics of 4 stages of P. sinica were investigated in the field and the critical dates for controlling these 4 stages with H. axyridis were investigated using predator exclosures. [Results]  Eggs, 1^st-2^nd instar nymphs, 3^rd-5^th instar nymphs and adults of P. sinica, had 3 generations from 23 April to 24 October. The average abundance of P. sinica was (71.0±11.8) per leaf. The average abundance of P. sinica inside, and outside, predator exclosures were (115.1±18.7) and (41.1±6.8) per leaf, respectively, which were, respectively, 1.62 and 0.58 times the species’ natural abundance in the field. The critical dates for controlling eggs, 1^st-2^nd instar nymphs, 3^rd-5^th instar nymphs, and adults, of P. sinica with H. axyridis were 20 June, 11 July, 23 May and 8 August, 13 June, and 19 September, respectively. The release of H. axyridis reduced the abundance of these life stages by 67%, 75%, 57% and 76%, 48%, and 79%, respectively. The post-release density of H. axyridis on each of the above dates was (3.0±1.0), (4.0±1.2), (4.3±0.7) and (3.0±1.0), (3.7±0.9), and (3.0±1.0) per plant, respectively. [Conclusion]  Successive releases of H. axyridis should be done to control different instars of P. sinica. The release of suitable densities of H. axyridis at the right time can effectively control P. sinica in the field.