Based on previous research on nanofiltration (NF) membrane, a new kind of flat Poly (m-phenylene isophthalamide)（PMIA）NF membrane was developed and used in removal of trace hazardous substances in water in this paper. The main research and conclusions are as follows: 1. A new kind of PMIA nanofiltration membrane was researched on non-woven in laboratory. The preparation conditions (PMIA concentration, evaporation time, additive proportion and membrane thickness) were optimized. A new kind of PMIA membrane was prepared and can provide a basis for industrial production. 2. The structure of the self-prepared membrane and two other kinds of NF membranes (ESNA1 and NF200) were characterized by scanning electron microscope, pore size distribution and streaming potential. The flux and salt rejection of self-prepared membrane were also measured. The results showed that the rejection reached up to 70%, flux reached up to 35Lm-2h-1 for 500ppm Na2SO4 system at 25℃, 0.5MPa. The some performances of self-prepared membrane could compare with commercial membranes. 3. The rejection of heavy metals such as Cr(Ⅵ) and As(Ⅴ) was investigated with self-prepared membrane, ESNA1 and NF200 membranes, respectively. The results indicated that Cr(Ⅵ), As(Ⅴ) could be effectively rejected by self-prepared membrane with 90% rejection. 4. The rejection of humic acid and trihalomethanes (THMs) were also investigated with three kinds of membranes. The results showed that rejection of small organic molecules (THMs) was low, but the rejection of macromolecules (humic acid) was relatively high by self-prepared membrane.