Due　to　the　excellent　features　of　environmental　friendly　and　energy　saving,　pure　electric　vehicles　are　getting　more　and　more　attentions　and　incentive　promotions　all　in　the　world.　Because　of　the　great　difference　between　engines　and　driven　motors,　there　will　not　be　engine　waste　heat　as　a　heat　source　for　the　air-conditioning　system　of　a　pure　electric　vehicle.　Though　a　direct　heating　device　can　be　used　to　solve　this　problem,　its　low　heating　efficiency　and　high　energy　consumption　unavoidably　makes　the　cruising　mileage　problem　serious.　Therefore,　differently　from　the　cooling　air-conditioning　system　in　traditional　vehicles,　it　is　obviously　a　good　way　for　an　electric　vehicle　to　use　a　heat　pump　type　air-conditioning　system　with　high　heating　efficiency.　For　a　heat　pump　air-conditioning　system　used　in　an　electric　vehicle,　the　frosting　of　evaporator　greatly　influences　its　heating　performance.　The　frost　characteristics　of　a　micro-channel　heat　exchanger　are　experimentally　studied　under　different　working　conditions.　The　influences　of　temperatures　and　humidity　on　the　frost　thickness　and　the　increment　of　ice　crystals　on　the　heat　exchanger　surface　were　studied　in　this　paper.　The　structure　of　frost　layer　was　investigated　with　CCD　imaging　technology.　A　program　based　on　MATLAB　was　made　to　study　the　growth　pattern　of　frost　layer　structure,　the　addition　of　ice　crystals　and　the　height　of　frost　layer,　with　wavelet　transform　and　gray　scale　threshold.　The　results　show　that,　the　lower　the　ambient　temperature,　the　more　the　amount　of　ice　crystals　is　and　the　more　the　frost　thickness　is;　keep　the　ambient　temperature　constant,　when　the　humidity　increases,　the　average　density　of　the　frost　layer　is　correspondingly　increased　and　the　distribution　of　the　ice　crystals　in　the　spatial　position　is　more　intensive.