Abstract: The evolution mechanism of IMT (Internet macroscopic topology) was studied in view of protocol. Analyzing mathematically the theory of protocol, a power-law star-like fractal topological reproducibility in IMT was obtained. A protocol-based mathematical model of IMT was developed according to physics and graph theory, by which the formula of topological reproducibility coefficient was deduced from transfer delay in network to determine the topology formation mechanism. Simulation tests were conducted to analyze the time sensitivity of the proposed model, and the results showed that the formation of Internet is a "ecological" evolution process from ordered simplicity to disordered complexity. Such a process can be attributed to that the limit value of the sum of topological reproducibility coefficients is a definite constant and, essentially, the design principle is to substitute the unlimited space of protocols for limited time effect.