The invention discloses a method of catalytically oxidizing unsymmetrical dimethylhydrazine wastewater under subcritical conditions. The method includes main technical parameters, equipment selection requirements and design parameters of a treatment apparatus set for treating wastewater being 15 L/h in flow rate. In the technical process, wastewater, under the subcritical conditions, is subjected to heating and heat exchanging so that the unsymmetrical dimethylhydrazine wastewater is treated through catalytic oxidization with a noble metal catalyst. The device is in a skid-mounted structure and mainly comprises an electric-heating apparatus, a heat exchanger, a catalytic reactor, a connection pipeline, an instrument valve, a safety valve, a water cooler, a gas-liquid separator, a control system and a pedestal. The catalyst is a noble metal composition catalyst. The system is high in safety and automation degree, can achieve auto-controlling, has the functions of automatic interlocking and manual operation control, is high in treatment capacity and is good in treatment effect, is strong in practicability and is high in maneuverability, can be arranged individually in a treatment site for treating wastewater and also arranged on a truck for treating wastewater, is good in economy and is low in energy consumption.