According to the fact that weak signals can not be accurately measured in the poor working environment,this paper proposed a high precision measurement circuit based on high accuracy instrumentation amplifier AD623,and can accurately amplify voltage signal ranged from 0mV to 25mV. The design also used a Precision optical isolator ACPL-C87B to isolate the affection of measurement to the collection.Through practical test, the weak-signal measurement circuit can achieve the accuracy of two percent. Also,the circuit has the characteristics of suppressing common mode interference, suppressing drifting, good stability and good ability of interference.