The invention relates to an assembly mechanism with a large diameter core inserted into a flexible rubber hose. The assembly mechanism comprises one or more guide push rods inserted simultaneously, aflexible rubber hose clamping mechanism, the large diameter core and a flexible rubber hose; the assembly mechanism is characterized in that the outer diameter of a first step of the front end of eachguide push rod is fit with the inner diameter of the large diameter core, and the front end of the first step is provided with a conical slope surface; the flexible rubber hose clamping mechanism iscomposed of two clamping sliding blocks of which the mirror images are moved relatively, and the relative inner sides of the clamping sliding blocks are provided with tension deviation preventing mechanisms; the inner diameters of the tension deviation preventing mechanisms are fit for the outer diameter of the flexible rubber hose; and each tension deviation preventing mechanism is made of elastic materials through machining. According to the assembly mechanism, the production stability and assembly efficiency of the whole intelligent automatic assembly line are improved greatly, and the production site and human resources are saved effectively.