By observing the internal quality of specimen of laser rapidly prototyping titanium alloy, I found that defects often appear in two places. One is the combing zone between the cladding and the substrate. The other is the area to be processed whose temperature field is unstable. In order to reduce the internal defect, this paper, taken a different way, puts forward an integrative method preheating and cladding all the way through laser, called Inverse Start Methods(ISM). According to the contrast test, the ISM combined with specific scanning can reduce the internal defects effectively.