An environmental monitoring pipeline closure and a wireless positioning and warning system thereof are disclosed. The environmental monitoring pipeline closure is composed of an upper platen, an expansion body, a lower platen, a plurality of bolts, and a plurality of compression rings, on which a plurality of clamping holes are provided for holding and fixing a cable line. A gas sensing device is provided inside the pipeline closure to detect gas concentrations within the space inside a manhole channel when being installed in the underground manhole channel. The measured data is transferred to a monitoring device through wireless transmissions to keep monitoring gas concentrations within the manhole channel. This prevents injuries and deaths of people working inside the manhole channel due to a lack of oxygen or inhalation of harmful gases.