Remarkable changes of physical and chemical properties are found in exposured 5-Nitroacenaphthene. which is usually used in negative photo-resists as a sensitizer. Analytical results demonstrate that 5-Nitroacenaphthene has undergone photo-reaction during the exposure. Its mainphoto-product is 8-Methy-4-Nitro-l-naphthealdehyde （C12H9NO3. or MNNA for short）. Using these changes of photo-induced properties of 5-Nitroacenaphthene. selective etching on SiO2 is realized and the mechamism of lithography without development is given satisfactory explanation.