Background Cubitus varus deformity (CVD), a common complication after a supracondylar fracture of the distal humerus, is usually treated with corrective osteotomy. However, due to the complex anatomy of the distal humerus, conventional osteotomy techniques are sometimes unreliable and can result in an inaccurate correction, residual deformity, and lateral condyle prominence. Recently, medial three-dimensional (3D) printing technology has demonstrated potential benefits for the treatment of CVD by improving the accuracy of the osteotomy through the use of an osteotomy guide with or without a patient-mated plate. This study aimed to present an interesting CVD case involving a patient who was treated with corrective biplanar Chevron osteotomy using an innovative customized osteotomy guide and a newly designed patient-matched monoblock crosslink plate created with 3D printing technology. Methods A computer simulation was processed using images from computerized tomography(CT) scans of both upper extremities. The biplanar Chevron osteotomy was designed to create identical anatomy between the mirror image of the contralateral distal humerus and the osteotomized distal humerus. Next, the customized osteotomy guide and patient-matched monoblock crosslink plate were designed and printed. A simulation osteotomy for the real-sized bone model was created. Results The operation was performed using the posterior paratricipital approach and the k-wire position from the customized osteotomy guide as a predrilled hole for screw fixation to achieve immediate control of the reduction after osteotomy. Our method helped successfully treat the CVD in the case study patient and significantly improved her radiographic and clinical outcomes with a satisfactory result. Conclusion This study showed that the treatment of CVD using 3D printing technology to create an innovative customized osteotomy guide and a patient-matched monoblock crosslink plate can help accurately assess and control the CVD correction. To the best of our knowledge, this case report introduces a new insight for the clinical application of 3D printing technology in the treatment of CVD.