A　double　wavelength　combination　and　long　focal　length　optical　system　was　designed　to　combine　and　focus　two　direct　high　power　laser　diodes　stacks　with　different　wavelengths　for　laser　material　processing.　First　of　all,　the　two　LD　stacks　were　collimated　by　fast　and　slow　axis　collimator　respectively.　Second,　the　two　LD　stacks　were　combined　by　double　wavelength　combine　mirror.　Then,　the　invert　Kepler　telescope　system　principle　was　applied　to　expand　and　collimate　the　laser　beam　in　the　slow　axis　direction.　Finally,　the　fast　and　slow　axis　laser　beams　were　focused　at　the　same　time.　The　focus　optical　system　was　analyzed　by　beam　parameter　product　theory,　and　the　focal　depth　was　also　be　calculated　by　Rayleigh　length　formula.　The　whole　optical　path　was　simulated　by　ZEMAX　software,　and　the　simulation　results　were　shown　after　ray　tracing.　Based　on　the　theoretical　analysis　and　ZEMAX　simulation,　the　corresponding　experiment　were　performed.　After　the　combination　and　focusing,　the　focused　spot　size　was　2.0　mm　×　4.0　mm,　and　focal　length　was　300　mm.　The　final　output　power　was　5　000　W　and　power　density　could　reach　to　104　W/cm2.　The　influence　factors　of　this　optical　system　were　discussed　finally.　The　focused　spot　can　be　applied　to　material　processing,　such　as　laser　cladding　and　surface　treatment.　©　2018,　Editorial　Board　of　Journal　of　Infrared　and　Laser　Engineering.　All　right　reserved.