A　high　power　optically-pumped　vertical-external-cavity　surface-emitting　laser　with　a　diamond　heatspreader　is　demonstrated.　Owing　to　the　good　thermal　conductivity,　diamond　can　accelerate　the　dissipation　of　heat　in　the　active　region　and　increase　the　output　power　significantly.　The　effects　of　the　curvature　radius,　the　transmission　of　output　coupler,　the　spot　size　of　the　pump,　and　the　temperature　of　the　heat　sink　on　the　output　power　are　investigated.　A　maximum　output　power　of　880　mW　is　obtained　under　the　conditions　of　10　degrees　C　temperature,　15-mm　curvature　radius,　3%　transmission　of　the　output　coupler,　and　8500-mW　pump　power.　The　slope　efficiency　and　the　optical-to-optical　conversion　efficiency　of　the　laser　are　about　17%　and　15%,　respectively.