Diesel engine tail gas selective catalytic reducing agent adding device and method

The invention discloses a diesel engine tail gas selective catalytic reducing agent adding method and a diesel engine tail gas selective catalytic reducing agent adding device with a simple structure. The diesel engine tail gas selective catalytic reducing agent adding device comprises a normally closed reducing agent storage container, an atomizing device which is arranged in the storage container and an atomized gas outlet which is arranged in the top part of the storage container. A negative-pressure pipe of a diesel engine tail gas pipe is communicated with the atomized gas outlet. The diesel engine tail gas selective catalytic reducing agent adding method comprises the steps that the atomizing device atomizes reducing agent into small-size atomized liquid drops, and when the liquid drops meet the negative-pressure pipe communicated to the diesel engine tail gas pipe, the liquid drops are absorbed and reach the diesel engine tail gas to realize selective catalytic reduction of nitrogen oxides in the tail