In order to solve the problem of collecting the residue of plastic film after potato harvesting, a combined machine was developed to dig potato and collect the residue of plastic film simultaneously. Based on the 4U?83 potato harvester, a crank-rocker mechanism was designed to strip the residue of plastic film and a cylinder device to collect and unload the residue of plastic film. The key parameters were calculated and determined for both of the devices. The shape and parameter of the shovel was improved to reduce the damage rate of potato and the efficiency of lifting and collecting the residue of plastic film. Field test showed that potato digger performed smoothly in digging and transporting with efficient separation. The plastic film can be rolled up continuously and reliably unloaded in convenient. The damage rate was 4.4% with the obvious rate of 96.4%. The recovery rate of the residual film was 89.3% with the film release rate of 98.1%. All of the parameters reached the requirements of technical specifications for design. The combined machine with digging and collecting functions achieved the same performance as the original potato harvester.