The automatic gas content apparatus was independently developed with no-pressure resistance and micro-pressure loss. It can not only continuously measure the content of shale gas，but also have the function of detecting methane concentration. Shale gas content at the well site was measured by this device in Southeast Chongqing.Continuous detection of desorbed gas composition was conducted for the first time，and it was found that the desorption of shale gas had unique characteristics. A“three-stage”variation type of gas desorption was obtained after core being sealed. In the early period（the first 3 hours），the methane concentration increased rapidly；and it became stable in the mid period（the next three to ten hours）；in the late period（from the tenth hour to the end），it decreased sharply with fluctuations. The shale gas desorption is a progressive process from the external to the internal，from fractures and large pores to microfractures，micropores and matrix of the shale. The released shale gas in the early stage was mostly from fractures or well-connected macropores，and the free gas was the main part. In the mid stage，the shale gas adsorbed in microfractures or macropores and that in mesopores with semi-connectivity and some micropores began to release，and the free gas and adsorption gas were the main part. In the late stage，the adsorbed and bounded gas desorbed from pores with poor connectivity and micropores，and the adsorption gas occupied the major part of the shale gas.