Abstract: A bismuth oxide material with a hierarchical structure in gas detection used for detecting the content of low-concentration ammonia in an environment. The bismuth oxide material with the hierarchical structure integrally presents a microsphere shape. The diameter of the microsphere is 1-3 ?m. The bismuth oxide material is formed by self-assembling lamellar structure units with the thickness of 10-80 nm. The bismuth oxide material is made into a gas sensor with high sensitivity and selectivity to ammonia gas at room temperature, which is suitable for detecting trace harmful gas in the environment. The gas sensor made of bismuth oxide does not need to be heated when in use, so that the heating step of the conventional gas sensor is omitted, and the gas sensor can be directly placed in a normal-temperature environment for operation. The method is simple, easy to operate, high in efficiency and wide in application prospect.