DMM is becoming more and more integrated, intelligentia high precisely and multifunctional, so the circuitry and program design of a kind of 4 3/4 digits DMM are introduced in this paper. This DMM is composed of DMM IC, single-chip TRMS/DC converter and single-chip computer. The instrument not only can measure TRMS voltage, but also have a number of remarkable characteristics: high measuring precision, wide measurement range, good function of measurement and changing measurement automatically, etc, which make it suitable for technological fields, such as modern electronic measurement, etc.