Abstract: In order to obtain lower- priced fuel oil,the feasibility of process for co- vis breaking to coal tar or biomass- oil and heavy oil was explored. The vis- breaking technology was mainly used for processing heavy oil from fossil oil,coal tar and biomass- oil mainly depended on the hydro- cracking of light and refined processing. By studying the mechanism of vis breaking to coal tar or biomass- oil and heavy oil,it was concluded that their reaction on vis- breaking had complementary advantages if they were subjected to co- vis breaking.More organic oxygen functional group were presented in coal tar or biomass- oil,they could become hydrogen donors and / or small free radical fragments generators with small molecular weight during vis breaking,the hydrogen donors and / or small free radical fragments were benefit to vs breaking to coal tar or biomass- oil and vis breaking to heavy oil. The co- vis breaking of coal tar or biomass- oil and heavy oil could improve the quality of coal tar,biomass oil and heavy oil,and get more light oil fraction,it also could greatly reduce the comprehensive processing treatment cost of coal tar or biomass- oil and heavy oil.