The simply constructed and easy operated device for measuring gas permeability of preservative film with concentration method was introduced together with its principle and method. A correction method of the measuring error coursed by sampling was put forward. It was put forward that during the measurement of gas permeability, gas sampling leads to pressure descent and loss of sample gas in the sample chamber, which brings to error of the determination result; to correct the error, total pressure in the sample chamber must be measured before and after every sampling.