Mitigation of high- energy particle radiation in space is necessary for executing long duration space missions successfully. Carbon based polymers and their composites are of huge interest in developing passive shielding techniques due to their high hydrogen content and lightweight nature. In this work, the radiation shielding properties of PEEK is evaluated in GCR free space environment using HZETRN. The total and particle wise dose equivalent is analysed in the human tissue. The variation in thermal conductivity of PEEK in is also studied based on the absorbed dose results. The optimization of the shield design considers a trade-off between mechanical integrity, particularly tensile strength, and its effectiveness in attenuating radiation. The objective is to develop a multi-layered shield with PEEK-W composite and Boron Nitride (BN) in order to get adequate structural integrity and effective shielding efficacy. It is found that PEEK - tungsten (W) composite, with an additional layer of boron nitride (BN) produces 2–4% greater reduction in dose equivalent in tissue as compared to traditional materials such as aluminum. Subsequently, the total shield thickness and tungsten concentration in PEEK are optimized. The results show that a radiation shield with PEEK composite containing 40% tungsten and a total thickness of 16 g/cm2 yields the lowest dose equivalent in tissue. Further, the energy spectrum after transport through the optimized shield is studied for different particle radiations such as proton and iron present in GCR spectrum. It demonstrates the viability of PEEK-W composite as an efficient shielding material for future space exploration.