Systematic, fixed_point and long observations and sample testing make clear distributions of methane and the homologues in the low_layer air over eastern China and sea areas. Within about 250 km from epicenter of moderate and strong earthquakes, oil_gas areas have methane concentration anomaly and CO-2 anomaly in the low_layer atmosphere around the earthquakes, have a temperature increase by 1-6℃ at the occurrence of moderate and strong earthquakes and indicate that concentration anomaly of methane family in the low_layer air can be used as an important index for petroleum geochemical exploration. Systematic, fixed_point and long observations and sample testing make clear distributions of methane and the homologues in the low_layer air over eastern China and sea areas. Within about 250 km from epicenter of moderate and strong earthquakes, oil_gas areas have methane concentration anomaly and CO -2 anomaly in the low_layer atmosphere around the earthquakes, have a temperature increase by 1-6 ° C at the occurrence of moderate and strong earthquakes and indicate that concentration anomaly of methane family in the low_layer air can be used as an important index for petroleum geochemical exploration.