Abstract: Aiming at the shortcoming of internal evolvable hardware dependent on professional hardware, this paper proposes a hardware evolving model, VHDLEM, based on the generative mechanism of VHDL. According to the different style of expression in VHDL, VHDLEM is divided two models, the condition action model, CAM, and the genetic programming model, GPM. In CAM, the truth table is encoded as binary sequence by using condition-judgment structure. If the target circuit has fewer inputs, the evolutionary of CAM can attain a higher rate. GPM is based on the logical expression in VHDL, in which the target circuit logical expression is converted to VHDL by means of genetic programming for the case that the target circuit has many inputs, the readability of VHDL evolved by GMP is better than that of CAM.