Provided is a device and a method for increasing a denitration inlet gas temperature. The low denitration inlet gas temperature can be easily caused by a prior heating surface disposition when a boil is in underload, thus a denitration device can not be put into operation, and the nitric oxide emission of exhaust gas exceeds the emission standard. The device for increasing the denitration inlet gas temperature is characterized in that: a first economizer (7) is installed on a rear smoke channel superheater of the boiler; the first economizer is connected with a first economizer inlet header (6); the first economizer inlet header is connected with a second economizer inter connecting tube (5); the second economizer inter connecting tube is connected with a second economizer outlet header (4); the second economizer outlet header is connected with a second economizer (3) installed on a denitration outlet smoke channel; the second economizer is connected with a second economizer inlet header (2); the second economizer inlet header is connected with a second economizer inlet tube (1). The device and the method are applicable to a heating surface disposition device for increasing the denitration inlet gas temperature.