Field experiments were conducted in China to analyse the reasons for maize yield decrease under plastic film mulching condition. The results showed that plastic film mulching significantly increased soil temperature, promoted maize growth and significantly sped up phenostages of maize. However, maize encountered a serious summer drought at the heading stage. The normal pollination of maize was affected seriously, which resulted in the decrease of maize yield. Maize yields with plastic film mulching were 73.6 and 12.9% lower than that of open-ground planting for 2 consecutive years. The frequency of serious summer drought was 15.9% at the maize heading stage in the experiment area, which resulted in maize yield decrease. These facts should not be ignored and need investigating. So plastic film mulching should be rationally chosen and applied in semi-arid areas according to concrete conditions.
