High temperature superconducting (HTS) generators are expected to pave the way to scale up offshore wind turbines to 10 MW and beyond. Although study of HTS wind generators has been of great interest and several designs have been proposed, the commercialization has not yet come. Despite the demonstrated feasibility and realized technical advantages, cryogenic cooling is still the key barrier to make the use of HTS technology in the field of offshore wind applications more transparent. In order to fulfill the requirements of handling, transportation, maintenance and reliability of long-term offshore operation, we have proposed a compact cryogen-free modular cryogenic cooling system for large scale HTS wind generators. The HTS generator usually contains many identical superconducting coils and each coil is allocated one identical modular cryostat in order to achieve the working temperature of 20-40 K. The modular cryostat enveloping the HTS coil adopts rectangular shape and consists of a vacuum vessel, a thermal shield with multi-layer insulation and corresponding supporting structures. Rods made of titanium alloy are selected as support structures to reduce the heat load. ... mehrA small scale two-stage Stirling or pulse tube cryocooler driven by oil-free linear compressor will be implemented in each modular cryostat to deliver the required cooling power.