Numerical study is performed to analyse the influence of aspect ratio on the nat-ural convection of high Pr fluid in a cavity with five discrete heaters at the bottom and an isothermalheat snk at the top,The range of aspect ratio is from 0.082 to 0.333, Raw is 107 and Pr is 90.Inthe half of the eavity five independent flow cells seperated by zero stream lines can be observed atsmall aspect ratio,which gradually merge into a single flow when aspect ratio increases and finallybeeome a big cell at A = 0.333.The average nusselt number based on the cooling arca,Nuc,showsthe highest value at A=0.082.With the incrcase of A,Nuc decreases and arrives the lowest valuewhile A=0.138,then increases and reaches an extreme value as A=0.164.After that Nuc fluctu-ates with the variation of increasing rate of flow velocity.