Anti-Reversing protection for persistent and high-insensitive software core algorithm has become an insistent demand for the research of software security and even for the whole software industry. Virtual machine based software protection has been widely used to protect the core algorithm from being reversed, but it is not sufficient for the current method to defend against cumulative attack and thus cannot provide long-term effective protection. Time diversity is used to fight against cumulative attack to allow software to execute along variant paths in different running time. A virtual machine based software protection method with time diversity, called TDVMP, is proposed in the paper. The key idea of the method is to construct multiple execution paths with equivalent semantics leading to dynamically variant execution paths in running time. Main design issues of TDVMP, such as construction and selection of multiple execution paths, are discussed in detail. Furthermore, a metric named variation of execution paths to evaluate the effectiveness of time diversity is proposed, and the methods to measure and compute the metric are also presented. A prototype of TDVMP is implemented, and upon which the experiments are carried out with a set of practical use cases. Experiment results show that TDVMP is effective and applicable for core algorithm anti-reversing protection.