The invention provides an estimating method and an estimating device of rock mass stability. The method includes steps of acquiring time information and intensity information of a slight shock event; determining the intensity distribution of the slight shock event according to the time information and the intensity information of the slight shock event; confirming revolution rules of a high energy slight shock event and a low energy slight shock event in the slight shock event on the basis of a dual-peak distribution model and the intensity distribution of the slight shock; estimating the rock mass stability of a working face according to the revolution rule of the high energy slight shock event and the low energy slight shock event. The method provided by the invention has the advantages of realizing the estimation of the rock mass stability, improving the accuracy of estimation, and guaranteeing the safety production of a mine.