Three pin-fin array with non-uniform diameters were considered for the purpose of cooling　characteristics optimization.　Combined method of transient liquid crystal technique test　and numerical simulation was employed to investigate　their heat transfer and pressure drop characteristics. The results showed that low pressure drop can be achieved when downsizing several rows of pin-fin diameters with a small cost of heat transfer loss. Within the Reynolds number from 10 000 to 50 000

the pin-fin array with 1.4-folds diameters ratio between odd and even rows caused just 6% decrease on average heat transfer factor

however

its friction factor declined as large as 21%.