Abstract : This report deals with the modeling and the global simulation of an autonomous microsystem. The aim was to propose a multi-level and multi-physics modeling methodology. We consider that this works takes place at the boundary between behavioral and physical modeling. To reach this goal, we have provided a library of VHDL-AMS implemented models for different blocks of a Wireless Sensor Network. These blocks belong to different domains of physics. The first block is a piezoelectric microgenerator which harvests mechanical energy and converts it into electrical energy to supply the other parts of the system. This block was modeled within different abstraction levels. A statistical analysis was performed to predict the impact of the process fluctuations on the structure performances. The second block is an energy storage system. An electrical model of a Li-Ion battery implemented in VHDL-AMS has been provided and simulated within different charge and discharge profiles and for different temperatures. A library of VHDL-AMS and SPICE models had been provided for the energy management block. Some of these models are valid for centimetric size systems, while others are more adapted to microsystems. Tow abstraction levels for this pure electrical block were considered : a technology independent level and a level related to the CMOS 120nm ST Microelectronics technology. In the last chapter, global simulations aiming to give an overview of the possibilities provided by this methodology were presented. In addition, comparisons with experimental results were proposed throughout this report.