Six kinds of Sn(OH)_4 precipitates were prepared by the chemical precipitation method (liquid-phase),of which the pH values are 3.0 (sample 1),4.5 (sample 2),6.0 (sample 3),7.5 (sample 4),9.0 (sample 5) and 10.5 (sample 6),respectively. After washed and dried,the Sn(OH)_4 precipitates were first calcined into tin oxide powder.Six kinds of gas sensors were made from the obtained SnO_2 powders.The XRD patterns of all the samples were recorded.The sensing properties of all samples to C_2H_5OH and H_2 gases were measured in different gas concentrations and temperatures,including the sensitivities of all samples,their response and recovery properties.The recovery properties of all samples to C_2H_5OH exhibit the sinusoidal oscillation character. Six kinds of Sn (OH) _4 precipitates were prepared by the chemical precipitation method (liquid-phase), of which the pH values ​​are 3.0 (sample 1), 4.5 (sample 2), 6.0 After washed and dried, the Sn (OH) _4 precipitates were first calcined into tin oxide powder. Six kinds of gas sensors were made from the obtained SnO 2 powders. XRD patterns of all the samples were recorded. Sensing properties of all samples to C_2H_5OH and H_2 gases were measured in different gas concentrations and temperatures, including the sensitivities of all samples, their response and recovery properties. The recovery properties of all samples to C_2H_5OH exhibit the sinusoidal oscillation character.