The invention discloses accelerator M modified alkylphenol-formaldehyde resin, and a preparation method and application thereof. The resin is obtained by carrying out a reaction on a reaction productof an accelerator M and chlorine with alkylphenol-formaldehyde resin under an alkaline condition. According to the invention, the accelerator M is used as a modifier, an intermediate compound Z whichcan easily react with resin is generated through a one-step reaction, and then the intermediate compound Z is mixed with the alkylphenol-formaldehyde resin for modification. The method provided by theinvention has a simple process and a high atomic utilization rate, adhesion performance of the obtained modified resin is obviously improved, performance of the modified resin is obviously better than performance of traditional tackifying resin, and tackifying durability and damp-thermal viscosity performance of the modified resin are obviously improved.