The invention provides an osmotic pressure molar density deternimator, comprising a base plate supporting the whole device, a left vertical plate and a right vertical plate, two refrigeration devices with same structures, a drive motor, a drive and transmission mechanisms, a movement positioning device and a control circuit board with a microprocessor, wherein the drive motor controls the movement of a sample holder, probes and probe search units. The effect of the invention is achieved as follows: the three straight line transmission mechanisms are driven by the drive motor and the drive motor respectively controls a temperature probe search unit, a stirring probe and the sample holder. Users can control the rotation direction and the rotation speed of the drive motor conveniently through utilizing the powerful control function of the microprocessor by keys, so that the automation control on the whole measuring process can be realized and the probability of incorrect manipulation brought by manual operation can be greatly reduced. The mechanisms have simple and compact structure, reliable and stable working, low noise and low failure rate, thereby greatly prolonging the service life of the osmotic pressure molar density determinator.