Aiming at the problems of the root of rice seedling were damaged because of the existing rice transplanting mechanism without mulch cutting device or the structure of the mulch cutting device was complicated causing poor synchronization and missing transplanting, the high-speed transplanter with extensible mulch cutting mechanism in the mulching cultivation system was designed based on the agronomic requirements of rice transplanting. The working principles of theoretical model was analyzed and a kinematic model of the rice transplanting mechanism was established. Computer-aided analysis and optimization software based on the Visual Basic 6.0 was developed and used to obtain a set of structure parameters and the trajectory of seedling-picking needle tip point and mulch cutting knife endpoint trajectory, which satisfied the transplanting requirements, the optimized parameters were as follows: seedling-picking angle was 16.01°, seedling-pushing angle was 62.43°, the mulch slit length was 44.31mm,the deviation of the mulch slit was 5.02mm, and planting position was 21.63mm. The 3D simulation model was combined with high speed photography test, the prototype machine test results were consistent with the theoretical analysis and virtual simulation results, the correctness and rationality of the design of extensible mulch cutting slit mechanism were verified. The soil bin transplanting experiment was conducted, the test showed that when the speed ratio characteristic coefficient was 1.57, the mechanism can finish cutting mulch and transplanting at the same time, the mulch slit length and plant location deviation of measured value with the theoretical values were less than 4mm, which reflected the practicality of the rice transpalnter with extensible mulch cutting mechanism.