Abstract: Like dual quaternion,double quaternion can be used in mathematic modeling of spatial mechanisms. The advantages of fast computing and robustness can be used in some special applications.So far,international journals have published some papers introducing this method,however,these methods need special mathematic knowledge and are not easy to understand. Based on the matrix method,the homogeneous transformation matrix can be divided into rotation and translation parts,and then the two parts are transformed into Hamilton operator. Double quaternion is then derived. By using the double quaternion,a small error will be introduced into the results,however,it can be controlled by the program. Another advantage is that it needs less multiply computing. A numerical example is given to verify the method,and this method can be easily understood.