Combined with the project design of the sector gate of the lower lock head of Yuxi first ship lock to be rebuilt and expanded，we research the static and dynamic optimal design of sector lock gate with a span of 34 m，which is the largest span in the sector gate of the domestic ship lock. Based on the finite element analysis and checking calculation of the preliminary design of the sector lock gate，we apply APDL of ANSYS to re-develop the 3D finite element model of the sector lock gate，and carry out the static optimization design and dynamic characteristic optimization with the aim of the minimum mass of the gate. The results show that by static optimization，the mass of triangular gate structure decreases 12.5% to 14.2%. Through dynamic optimization，the first order natural vibration frequency of gate is improved，which meets the constraint condition of not less than 5 Hz.