The effectiveness of a method to improve the precooler performance under frosting condition was investigated by experiments on a sub-scale heat exchanger model. Addition of a methanol proved to be most effective compared with other possible substances in both cases of low and high cooling wall temperature. Then the effectiveness of the methanol addition was ascertained for the practical condition that means the same tube configuration and flow velocity as the precooler designed for the ATREX engine firing test model. The result showed that the addition of the same quantity as the water vapor could restrain the frost layer from choking the flow in the duration of 300 seconds, which is sufficient time for precooler operation. The required methanol mass along the ATREX engine flight path was estimated to be less than 3% of fuel hydrogen on board. Accordingly, the method came to be promising candidate for practical application.