This paper presents a design and simulation for the voltage sag monitoring technique that intends to apply to multi-point measurement in a power transmission system. The purpose of this research is to fabricate a mixed-signal processing unit especially for power quality monitoring. The system modeling shows the framing discrete wavelet transform proves that the decision making for the voltage monitoring can be faster than the root-mean-square calculations. Also, analog integrated circuit for the data acquisition and digital integrated circuit for the discrete wavelet transform are designed and simulated in this paper. The voltage sag waveforms tested in this research project are obtained from IEEE P1159.2. They are categorized into two different cases: voltage sag caused by a single line-to-ground fault and interruption preceded by voltage sag.