Lung cancer (LC) is the leading cause of cancer-related deaths worldwide. MicroRNAs (miRNAs) are highly evolutionarily conserved noncoding small RNAs, which were first identified in Caenorhabditis elegans. There are 1100 or more miRNAs have been identified in Homo sapiens. Let-7 miRNA is involved in the regulation of gene expression in cells. Several novel factors and feedback loops involved in the regulation of the synthesis of let-7 have been identified and additional let-7 target genes have been found. Let-7 has also been shown to be significantly correlated with the occurrence and development of cancer and the results of preliminary studies suggest that it is involved in the regulation of oncogenic pathways in numerous types of tumors, such as, LC. As let-7 is a potential molecular target for tumor therapy, a mass of studies have been conducted focus on the relationship between let-7 and LC. With the mechanism becoming revealed, more and more groups are looking for the anti-tumor role of let-7 family in anti-tumor therapy development. In this review, we summarize the newest investigations on let-7 and LC, the regulation of let-7 and its targets gene have been discussed, and the attempts for new therapy for LC have also been summarized.