The invention discloses a 
hybrid machine tool milling stability prediction method. The method comprises the steps of integrally dividing a 
hybrid machine tool 
system into a cutter, a cutter 
handle, amain shaft and a parallel / parallel 
hybrid mechanism, the cutter-cutter 
handle-main shaft serving as a first sub-structure, and the parallel / parallel hybrid mechanism serving as a second sub-structure;measuring to obtain 
frequency response functions of the first sub-structure and the second sub-structure, and obtaining a tool 
nose point 
frequency response function; establishing a milling kinetic equation under a physical coordinate 
system; converting the milling kinetic equation under the physical coordinate 
system into a milling kinetic equation under a 
modal coordinate system; solving a milling kinetic equation under the 
modal coordinate system to obtain a 
state transition matrix; judging the characteristic value of the 
state transition matrix, and drawing a stable lobe graph; and carrying out milling stability prediction on the parallel hybrid 
machine tool system according to the stability lobe graph. According to the method, the influences of the low-order dynamic characteristics and the medium-high-order dynamic characteristics of the parallel mechanism are comprehensively considered, and the milling stability of the parallel hybrid 
machine tool can be predicted more accurately.