The field population activity of meadow moth,(Loxostege sticticalis L., generally occurred on night time. The most frequent activity of adults occurred in the vegetation with abundant forage plants from 21 o’clock to midnight. Adults laid eggs on a lot of weeds and crops, and most eggs were laid on the middle or lower part of plants. Most of the larvae inhabited or fed on the egg host plants before they were the third instar. The width of cephalosome and baenosome and the length of cirpus of the larvae in every instar were determined. These larvae were separately fed under the condition of constant temperature of 20℃ and30℃. The distinguish methods of different larvae stage were put forward, i.e. which was on the basis of the cephalosome width with the cirpus length or baenosome width. It was suggested that the field survey of larvae occurrence should lay particular emphasis on the vegetation of frequent occurrence of adults or abundant host plants of larvae.