Large　core　diameter　crystal　waveguides　can　absorb　higher　power　pump　light　and　achieve　higher　output　power.　At　the　same　time,　the　peak　power　density　in　the　core　layer　is　relatively　low　during　mode-locking　operation,　and　the　accumulation　of　nonlinear　effects　is　reduced.　Based　on　this,　a　passively　mode-locked　picosecond　laser　based　on　Yb:　YAG　large　core　diameter　crystal　square　waveguide　is　constructed.　In　the　experiment,　firstly,　the　high　mirror　is　used　instead　of　the　semiconductor　saturable　absorption　mirror　(SESAM),　and　the　position　and　angle　of　the　crystal　waveguide　are　adjusted　to　match　the　pump　light　with　the　waveguide　core　layer　under　higher　pump　power.　Then,　the　angle　of　the　spherical　mirror　is　carefully　adjusted　to　couple　the　signal　light　into　the　waveguide　core　layer　to　minimize　the　loss　in　the　cavity.　The　designed　laser　adopts　a　folded　cavity　structure,　and　achieves　an　average　power　of　10.2　W,　pulse　width　of　65　ps,　repetition　rate　of　30.15　MHz,　and　single　pulse　energy　of　0.34　mu　J　without　dispersion　compensation　device.