【Propose】This work has been done in order to solve the problems of long time consuming， complex operation， and poor environmental applicability of the existing methods for detection of calcium hydroxide absorption rate in emergency rescue work.【Methods】A method to invert the avail⁃ability of calcium hydroxide by using acoustic velocity was proposed. By measuring the change of acoustic velocity in calcium hydroxide sample， the residual CO2 absorption rate was determined， and the availability was evaluated according to coal industry standards. On the basis of the experiment of CO2 absorption by calcium hydroxide with time， the law of CO2 absorption by calcium hydroxide with time was discussed. This variation rule is caused by the combination of the product CaCO3 coating barrier to the inward CO2 diffusion and the continuous reduction of the effective volume of calcium hy⁃droxide sample along with the continuous reduction of the contact surface between Ca（OH）2 and CO2. According to the test experiments of calcium hydroxide absorption rate and acoustic velocity， a mathematical model for judging the available of calcium hydroxide by acoustic velocity is established.【Findings】The test results show that the relative error of the test results is less than 1% with a single test time of 1 to 2 min， which achieves high efficiency and high precision test of calcium hydroxide absorption rate