By using anionic surfactant to foam monomer casting nylon 6 (MCPA6), MCPA6 with foam cell was prepared so as to make the material lightweight. The cell structure of the material was observed by scanning electron microscopy (SEM), and its properties were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results showed that the shrinkage of MCPA6 foamed with sodium dodecyl sulfate (SDS) decreased remarkably by forming a series of pores, which promoted the movement of the molecular chain of MCPA6 and increased its crystallization rate, while inhibited the formation of the gamma crystal form of MCPA6 and reduced the crystallinity of the material. The inhibition of foaming on the crystalline form and the decrease of crystallinity of MCPA6 were beneficial to its absorption of impact energy.