A motor case assembly includes a shaft and a motor case. The shaft has a connection end formed with a groove. The motor case has a perforation for assembling and connecting with the shaft. A hub section protrudes a rim of the perforation and has a forced outer face and an inner face surrounding the connection end and the groove of the shaft. An external means is used to apply an external force to the hub section so as to make the hub section tightly hoop the connection end of the shaft. By means of the external force, the inner face of the hub section is partially intruded into the groove of the shaft to form an intrusion body connected with the groove under a top wall inner face of the motor case. Therefore, the motor case and the shaft are securely connected with each other without easy detachment.