The invention discloses a width-adjustable assembly platform of a radiator core assembly machine. The assembly platform comprises an assembly platform body formed by arranging a plurality of base plates in parallel and a supporting assembly supported at the bottom of the assembly platform body. A plurality of elastic pieces capable of strutting the adjacent base plates at equal intervals are arranged between the base plates. A connecting limiting piece capable of limiting the maximum stretching width of the adjacent base plates is connected between the base plates in a penetrating mode. The left ends and the right ends of the supporting assembly and the assembly platform body are connected with main board profiling workbenches respectively, and under driving of the two main board profiling workbenches, the supporting assembly at the bottom of the assembly platform body and the assembly platform body can stretch out and draw back synchronously to adjust the width. According to the width-adjustable assembly platform, the width can be synchronously adjusted along with the two main board profiling workbenches, then the defect that the assembling specification of a core of an assemblymachine is limited is overcome, the adjusting process is simple, synchronous adjustment along with the two main board profiling workbenches is achieved, and the automation degree is high.