Currently, optical communication network is developing rapidly towards large scale and large capacity. Higher request in optical fiber communication system is put forward to face with the huge pressure of transmission bandwidth. Under this background, multicore fiber (MCF) based on space division multiplexing (SDM), overcomes the congestion problem caused by the theoretical transmission limit of single mode fiber. Multicore fiber cannot be used in the transmission system only if it has the optical properties of low crosstalk and large effective area. Intensive simulation work based on beam propagation method (BPM) and finite element method are performed to find out key parameters which have a great influence on crosstalk and effective area in multicore fibers, which are used in the experiment to prove the correctness of simulated results. The designs of core pitch, the size and the refractive index of core and trench are optimized simultaneously to theoretically achieve optical properties suitable for the future large capacity transmission with low crosstalk less than -45 dB after 100 km and large effective areas larger than 130 μm2.