A polyurethane used for orthopedics external fixing system in complex environment is obtained by reaction of mixture of polyether polyol with modified isocyanate in the weight ratio of 1:0.6-0.75. The modified isocyanate is obtained by reaction of polyphenyl polymethylene isocyanate with polyether diol. The components and corresponding weight percents of the mixture of polyether polyol are as follows: 60-65% polyether polyol as shown by formula (I), in the formula, m is an integer of 7-15, R represents mannitol, sucrose or pentaerythritol 0.3-1% catalyst 0.1-2% foam stabilizer 0.1-2% or 3-20% foaming agent 25-40% filler and 0.5-2% functional auxiliary agent. The method of producing the polyurethane is also provided.
