The invention discloses a fertilizing device for returning rice straw to the field. The device comprises a rack, a transmission mechanism is arranged at the left end of the rack, a straw cutting conveying device is connected to the left end of the transmission mechanism, and a straw guide tube is connected to the right end of the transmission mechanism; the outlet of the straw guide tube is connected with the inlet of a chopping device, a sowing tube is connected to the outlet of the chopping device, and a sowing device is connected to the lower portion of the sowing tube through a vertical pipeline; a secondary smashing device, namely a cutting device is arranged additionally, through cutting and smashing of horizontal helical cutting blades and sowing helical slices, the straw which is conveyed by the straw cutting conveying device can be cut into smaller.