The invention relates to an organic solar cell material and a preparation method thereof, particularly a novel organic solar cell material based on thiophene-diazosulfide p-n structure and a preparation method thereof. The quantities and contents of the p-type electron donating primitive thiophene and n-type electron receiving primitive diazosulfide are regulated to precisely regulate the band gap of the target material, and the alkyl chain is modified to implement solubility in a polar solvent and application in the field of organic photoelectricity. The structure is disclosed as Formula I. According to the material provided by the invention, Suzuki reaction is utilized to synthesize the monomer, and the material is simple in synthesis technique, easy for mass production and easy to purify. The material has favorable spectrum heat stability, amorphous film-forming stability and narrow optical energy gap, can absorb sunlight within a wider wave spectrum range, and can be used in organic solar cell devices as an active material.