The　direct　solar　drying　system　has　the　advantages　of　simple　structure,　cheapness,　and　protecting　the　dried　materials　from　being　damaged　by　dust,　rain,　dew,　and　so　on;　however,　there　are　some　disadvantages　such　as　overheating　of　the　dried　materials　surface,　poor　quality　of　the　dried　material　and　drying　ability　limited.　In　order　to　solve　problems　of　drying　product　overheating　and　drying　process　uncontrollable　in　direct　solar　dryer,　a　direct　solar　drying　system　was　designed　and　built　to　test　system　performance　by　using　sweet　potatoes　as　drying　material.　The　system　was　mainly　composed　of　air　inlet,　air　outlet,　dry　material　tray,　transparent　glass　cover　and　stainless　steel　plate.　The　frame　of　drying　chamber　was　made　of　aluminum　alloy,　and　the　black　endothermic　material　was　uniformly　applied　to　the　inner　surface　of　the　stainless　steel　plate　of　the　drying　chamber.　The　tilt　angle　of　the　roof　glass　of　the　drying　chamber　was　26.7°.　The　length,　width　and　height　of　the　drying　chamber　were　1000,　800　and　800　mm,　respectively.　The　insulation　material　of　the　drying　chamber　was　made　of　20　mm　thick　polyurethane　insulation　cotton　to　prevent　the　heat　loss,　and　the　transparent　surface　of　drying　chamber　adopted　ordinary　glass　with　transmittance　of　90%.　The　dry　material　used　in　this　experiment　was　fresh　sweet　potato,　purchased　in　Jingdong　Mall,　with　the　origin　of　Yuxi,　Yunnan.　Before　the　experiment,　the　sweet　potatoes　were　cut　into　pieces　of　uniform　size　and　thickness,　and　divided　into　2　parts　with　the　same　mass　by　the　balance;　one　part　was　used　for　the　experimental　group　of　direct　solar　drying　and　the　other　part　was　used　for　the　comparison　group　of　open　sun　drying.　The　experimental　test　was　conducted　on　May　7,　2017,　from　8:　30　to　17:　00.　The　initial　mass　of　dry　materials　in　the　experimental　group　and　the　control　group　was　240　g.　In　addition,　dynamic　mathematical　models　of　thermal　performance　of　system　were　built　and　calculated　with　the　help　of　MATLAB　2014a　software,　outdoor　meteorological　parameters,　the　characteristics　of　drying　materials　and　building　systems　were　given,　and　the　correlations　between　experimental　value　and　simulation　value　were　analyzed.　The　results　showed　that　the　transmittance　of　drying　chamber　ranged　from　51.7%　to　89.6%.　The　highest　air　temperature　in　the　drying　chamber　appeared　half　an　hour　later　than　the　peak　of　outdoor　solar　radiation　intensity.　It　indicated　that　the　drying　chamber　had　certain　delay　and　resistance　to　the　change　of　outdoor　environment　interference.　The　average　drying　rate　of　the　direct　solar　drying　system　was　7.7　g/h　higher　than　that　of　the　open　solar　drying　system.　Time　period　with　drying　air　temperature　ranging　from　50　to　70　accounted　for　80%　of　the　total　drying　time,　which　showed　that　the　direct　solar　drying　system　can　provide　the　most　suitable　drying　temperature　for　most　dry　materials.　The　total　thermal　energy　obtained　by　the　drying　system　was　3.92　kW·h,　and　the　average　solar　heat　utilization　efficiency　was　21.23%;　the　correlation　coefficient　of　the　experimental　value　and　the　simulated　value　was　0.98,　and　the　root　mean　square　error　was　1,　which　proves　that　the　dynamic　model　of　dynamic　thermal　performance　can　accurately　predict　the　surface　temperature　of　the　dry　materials　in　the　drying　chamber.　©　2018,　Editorial　Department　of　the　Transactions　of　the　Chinese　Society　of　Agricultural　Engineering.　All　right　reserved.