It is difficult to “cap” cement in the lost circulation formation of geothermal wells. In most cases， the well cementation is failure due to the deviation of the squeezed cement slurry from the design position. In this paper， the technical idea of “cap” cementation in lost circulation zone is proposed， that is， the moving position of the cement slurry column is effectively controlled by balancing the fluid column pressure in the well with the formation fracture pressure， and the cement slurry is prevented from being diluted by controlling the displacement of squeeze injection. Open cementing and closed cementing methods can be both used in practice. The open cementing is suitable in the condition that the difference of the casing lever among the upper parts and the lower parts is small especially in same level. The shaft is always connected with the outside air and the upper and lower shaft always connected in the process of slurry injection. The cement slurry column moves down a long distance during the balancing process and is easily diluted， and the position of the slurry column is difficult to control when the upper casing is quite different from the lower one. However， the required tools are simple. The closed cementing is suitable for any casing matching requirements， especially for the larger casing grade difference. For this method， special sealing tools shall be used to seal the lower casing， the upper and lower wellbore are impassable during cementing， which could avoid the disadvantages of long downward distance of cement slurry column， difficult position control and easy dilution， etc.