Porous glass was prepared by thermally treating sodium borosilicate glass for different time,the effect of thermal treatment on pore size distribution was discussed and the pore size of the prepared porous glass was measured by scanning electron microscopy (SEM) and differential thermal analysis (DTA). The results show that the optimum porous glass with an average diameter of 80 nm can be prepared by thermal treatment at 600 ℃ for 12 h and then acid treatment for 12 h in 2 mol· L-1 hydrochloric acid solution.