Digital modulation and demodulation techniques in a digital communication system has a very important position, FPGA has become today's electronic design applications market preferred one of the programmable logic device; not all fields FPGA nowhere in the scene. With advances in electronic technology, FPGA performance of the year in improving; making FPGA devices compared with other more competitive; digital communication technology and FPGA combination of modern communication systems development a natural trend. VHDL is a description of digital electronic systems in the language, It originated from the United States government's very high-speed integrated circuit (VHSIC) program. VHDL design process to meet the various needs; In this paper, using VHDL for FPGA modulation and demodulation system design. This paper introduces the ASK, FSK, QPSK modulation and demodulation in principle; Based on FPGA ASK, FSK, QPSK modulation and demodulation circuit. Using VHDL programming respectively to achieve ASK, FSK, QPSK modulation and demodulation; and the use of Altera Corporation to launch a complete integrated design environment QuartusII compile simulation; thus proving the correctness of the design. VHDL is a powerful language; Reader - friendly, easy to modify and found errors; Strong portability; low cost; Design and Technology has nothing to do n; transplantation; can be used for simulation of VHDL source code for functional simulation; But for beginners easily make mistakes, the algorithm needs to be constantly testing simulation certification.