A new type of reactor, featured with impinging stream-rotating packed bed (IS-RPB) and coil pipes, was designed and used to prepare p-hydroxybenzaldehyde (PHB) by hydrolysis from diazonium salts. The influence of operating parameters, such as reaction temperature, reaction time and high gravity factor, on the yield of PHB was investigated. Compared with the traditional kettle-type reactor, the yield of PHB with the new reactor is increased significantly and the reaction time is much shorter. Under the optimum conditions, the yield of PHB is increased from 51% to 84.1%. The reactor offers an opportunity for replacing the traditional batch mode operation with a continuous process.