A　novel　fuzzy　PID　control　strategy　of　Buck　converter　system　with　double　closed　loop　structures　is　proposed　to　solve　problems　that　complex　control　objects　are　difficult　of　modeling　and　the　artificial　tuning　experiences　are　lack,　etc.　The　voltage　and　current　loop　structures　are　designed　to　improve　both　the　anti-disturbance　performance　and　the　following　performance　of　the　system.　A　membership　function　that　combines　the　Gauss　function　and　the　triangular　function　is　selected　to　enhance　the　sensitivity　of　the　controller　to　small　error.　Three　sub　inference　devices　are　designed　based　on　the　PID　parameters　and　the　rule　base　of　expert　experiences,　and　the　fuzzy　rule　of　Buck　converter　is　developed　to　make　the　designed　controller　independent　of　the　precise　mathematical　model　of　Buck　converter.　So　that　it　overcomes　the　high　percent　overshoot,　oscillation　and　other　shortcomings　of　the　output　voltage　caused　by　traditional　PID　controls.　A　new　Buck　converter　system　of　double　closed　loop　circuits　is　designed,　and　the　fuzzy　PID　control　strategy　is　applied　to　control　the　quantities　with　rapid　change　and　small　time　delay　by　making　use　of　STM32.　Experimental　results　show　that　the　fuzzy　PID　control　strategy　not　only　improves　the　tracking　accuracy　of　the　output　voltage,　but　also　effectively　suppresses　the　load　disturbance　and　parameter　perturbation,　and　that　the　overshoot　of　the　output　voltage　is　less　than　10%　and　the　adjustment　time　is　less　than　3　ms　under　the　step　to　start.　A　comparison　with　the　traditional　PID　system　show　that　the　designed　system＇s　output　voltage　ripple,　maximum　dynamic　voltage　drop　and　recovery　time　under　the　disturbance　are　reduced　by　one　order　of　magnitude.　©　2016,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.