The invention relates to a continuous preparation system and a preparation technology of whole grain grade tailing cemented filling slurry. The continuous preparation system mainly comprises a tailing slurry collecting buffer feeding device, a deep-cone thickener, a flocculating agent preparing and adding device, an underflow slag slurry pump, a cementing material storage bin, a cementing material measuring and conveying device, an air compression system, a water supply system, a filling accident pool, a stirring system and a filling slurry output pipeline. The preparation technology comprises the steps of conveying tailing slurry to the tailing slurry collecting buffer feeding device through the slag slurry pump, after reducing the pressure to 0.03 MPa through the collecting buffer feeding device and carrying out energy dissipation, feeding the tailing slurry into the deep-cone thickener, and adding a flocculating agent into the deep-cone thickener according to the principle that for per ton of tailing slurry, every 5 to 20 g of the flocculating agent is added, so as to obtain high-concentration tailing slurry with the concentration of 65 to 75%; and conveying the high-concentration tailing slurry and a cementing material into the stirring system according to the fact that the mass ratio of the high-concentration tailing slurry to the cementing material is 1 to (5 to 40), adding water, stirring, and preparing the mixture into the high-concentration whole grain grade tailing cemented filling slurry with the concentration of 65 to 75%. According to the continuous preparation system and the preparation technology, the system is simple, the automation degree during the preparation process is high, the operation is convenient, and the filling slurry can be continuously prepared.