Letrozole is a highly effective non - steroidal aromatase inhibitor that reduces estrogen levels by inhibiting aromatase activity. It has important application value in the field of fertility preservation，especially in patients with malignant tumors. For patients with estrogen-sensitive malignant tumors such as breast cancer，letrozole can reduce the concentration of circulating estrogen in the body during ovulation induction，thereby reducing the adverse effects of high estrogen on tumors during traditional ovulation induction，and effectively promote follicular development. However，the low estrogen level environment in the body brought about by letrozole may lead to decreased oocyte maturity or embryo quality and reduced embryo implantation rate. Further large-scale clinical studies are needed in the future to clarify its long-term safety and efficacy in fertility preservation，and provide more precise treatment strategies for fertility preservation in patients with malignant tumors.