A long-term storage test under constant temperature of 3℃ was carried out to undiapause Trichogramma dendrolimi of six stages of growth including young larvae, middle larvae, old larvae, prepupa, initial pupa, middle pupa. The results showed that the storage effect was influenced by different stage of growth. The middle larva is the best stage and young larva is better stage for storage. The storage time of young larvae and middle larvae may not exceed sixty day, others may not exceed fifteen days. As the storing lasted, the number of Trichogramma dendrolimi in a single host egg reduced in first twenty days. Later, it no longer changed. If young larva was stored, the number of Trichogramma dendrolimi in a single host egg reduced greatly. The change of the single female adult oviposition was not significantly correlated with the length of storage. In case initial pupa and middle pupa were stored, the number of the single female adult oviposition reduced greatly.