Abstract: From the theory that four-connecting rods mechanism has flexibility and any closed graphics of plane mechanism has three restrictions,the calculating formula of degree of freedom of mechanism is researched. The results of research indicate that the calculating formula of degree of freedom of space mechanism will be set up if the calculating formulas of degree of freedom of plane and spherical surface mechanism are changed a little. The new formula could substitute for 29 traditional calculating formulas of degree of freedom of space mechanism. The new formula is suitable for not only space mechanism but also the plane mechanism, the multiple rings space mechanism, the open chain space mechanism and mixed chain space mechanism and so on. Because that the new formula is easier and rapider in use than traditional formulas, it is a reliable theoretical calculating formula for calculating degree of freedom of space mechanism.

Key words: Number of restrictions Number of closed rings, Space mechanism Degree of freedom