An air fan module and a flow directing blade assembly thereof aim to reduce noises generated during operation of the air fan caused by friction between blades and air and improve cooling efficiency. The air fan module includes a fan frame which has an air inlet, an air outlet and a housing space formed between them to hold a flow directing blade assembly. The flow directing blade assembly has an axis and a plurality of blades mounted onto the axis. Each blade has a first end surface and a second end surface. The first and second end surfaces have respectively a plurality of first flow directing portions and second flow directing portions that are respectively spaced from each other and formed in an asymmetrical manner. Air can form steady airflow by channeling of the first flow directing portions and the second flow directing portions of two neighboring blades.