The electrochemical C V profiler and the current voltage(I V) characteristics analysis was used to study the influence on doping Mg in AlGaInP with MOVCD growth.Through the electrochemical C V profile,we analysed the density of Mg in the AlGaInP growth structure,and used the I V characteristics to analyse the structure of the AlGaInP LED device,then found an abnormal result.From computing and theory analyzing the structure of the homotype junction (N + N,P + P),we got the height of the homotype junction barrier and the width of the space charge region,and analysed the doping density difference between both sides of the homotype junction.It excellently explained the abnormal I V characteristics result.