Migratory insects make diverse adaptive strategies in response to changes in external environment.  Temperature has an impact on the survival, development, reproduction, and migration initiation of insects.  Previous research has primarily been focused on the effects of constant temperature on populations, but changing temperature has received less attention.  Three constant temperature treatments (20, 25 and 30°C) and three pupal-alternating temperature treatments (20–25, 25–20 and 25–30°C) were set up to study the relationship between temperature and population development by age-stage, two-sex life table analysis in the oriental armyworm, Mythimna separata Walker, a notorious migratory pest in grain crops.  The 25°C treatment was considered optimal with 20 and 30°C as low suitable temperature and high temperatures, respectively.  The survival rate was relatively low before third instar larvae at  20°C (63.0%) and 20–25°C (70.1%), and extreme low after pupal stage at 30°C (20.6%).  Developmental duration of each stage was negatively correlated with temperature.  The adult pre-oviposition period, when most migratory insects initiate migration, was the shortest at 25°C (2.69 d) but was lengthened at both low suitable (7.48 d for 20°C, 6.91 d for 25–20°C and 4.57 d for 20–25°C) and high temperatures (3.74 d for 25–30°C and 5.00 d for 30°C).  Both low suitable and high temperature decreased lifetime fecundity, net reproductive rate and the intrinsic rate of increase, with variability observed across developmental duration and stage during non-optimal temperature.  The results expand knowledge of the relationship between changing temperature and armyworm population development, and adaptive strategies in complex ambient environment.