The invention discloses an unstable flow liquid online flow measuring device and belongs to the field of flow measuring. The device comprises a heat insulation explosion-proof device, a water storing device, a metering device, a controller, a valve, a valve transmission device, a liquid level detecting device, a liquid level detecting device, a heating device, a display device, a communication port and a mains supply input port. One side of the device is connected with 220V mains supply input, the other side of the device is connected with an upper computer through the communication port, the communication display device and a junction box 1 are fixed on an outer wall on the upper portion of the heat insulation explosion-proof device, the water storing device, the metering device and the controller are all arranged in the heat insulation explosion-proof device, and the heat insulation explosion-proof device is provided with a liquid input port and a liquid output port which are connected with a pipeline of liquid to be measured. Accurate measuring and adjusting on liquid flow guarantees safety and economical operation of a production process, improve product quality, reduce material consumption, improve economical benefit and lay a foundation for achieving scientific management.