Abstract:The community structure and population dynamics of natural enemy, the dynamics of Aphis gossypii and natural enemy and the control effect against Aphis gossypii in cotton-alfalfa intercrop fields were studied using different cotton-alfalfa intercropping methods. The results showed that population density of ladybirds, spiders and lacewings had increased rapidly in cotton-alfalfa intercrop fields. The population density of ladybirds, spiders and lacewings had respectively increased 318.0%, 120.9% and 79.6% in intercropping fields of 75cm-wide alfalfa belt within 1.6m-wide cotton belt. The species richness, richness index and diversity of natural enemy community were higher in cotton-alfalfa intercropping or neighbor crop field than that of in normal cotton field. This implied that natural enemy community abundance and diversity in cotton field could be increased by intercropping and neighbor crop and cutting alfalfa belt at proper time. Cutting alfalfa belt could affect the population dynamics of ladybirds, spiders and lacewings. Cutting the alfalfa belt during the A.gossypii population increasing period, the population density of ladybirds, spiders and lacewings had been increased and A.gossypii had been decreased rapidly, as a result, it could control the outbreak of A.gossypii in cotton fields effectively.