Natural gas is rich in shallow-buried Devonian-Carboniferous and Permian-Triassic reservoirs in Guizhong Depression. Natural gas generally consists of hydrocarbon gas, CH4, and non-hydrocarbon gas, CO2 and N2. Gas presents obvious differentiation of components from north to south and as a result N2 is getting rich and reaches up to 80,-90, of volume fraction in the area of wide-exposed Carboniferous reservoirs. Hydrocarbon gas is relatively rich in the area of residual Permian-Triassic reservoirs. For instance, CH4 is coexistent with CO2 with equivalent volume fractions in Well GZ1 in the central of depression but southwards the CH4 may accumulate to 80, of volume fraction in Well D907. It is shown that the CO2 is derived from carbonate rock by decomposition of deep hydrotherm and the N2 commonly comes from atmosphere, which is relative with karstification by infiltration of surface fresh water. It is suggested that the differentiation of gas components in spacial distribution are the result from different preservation conditions in this depression. Different gas components are the evidence of gas accumulation and preservation.