The utility model provides a variable frequency motor encoder installation interface modular design structure, which comprises a motor rotating shaft, a bearing outer cover and an encoder, the middlepart of the bearing outer cover is provided with an extended cover neck part, the outer end of the cover neck part is provided with a cover opening, an encoder transition plate is fixed on the cover opening of the bearing outer cover through a bolt, and the encoder is installed on the encoder transition plate; a motor rotating shaft is connected with the shaft sleeve, and the shaft rod end of theshaft sleeve is connected with a rotating shaft of the encoder. The shaft sleeve comprises a sleeve opening and a shaft rod end, the sleeve opening thermally sleeves the tail end of the motor rotatingshaft, and a rotating shaft of the encoder sleeves or is connected with the shaft rod end through a coupling. Wherein the encoder transition plate is disc-shaped, the middle part of the encoder transition plate is a stepped hole for installing an encoder, the encoder is fixed on the encoder transition plate through screws, the inner side of the encoder transition plate is provided with a circulartruncated cone butted with a cover opening of the bearing outer cover, the circular truncated cone sinks into the cover opening, and the periphery is provided with installation holes which are connected with the transition plate installation holes through bolts and fixed on the cover opening of the bearing outer cover. According to the utility model, the modularization of the connection part of the motor and the encoder is realized, and the versatility of parts is enhanced.