In the present paper, we use 10 plate pairs, for which the time baselines are from 16 to 70 years, to obtain the relative proper motions of 872 stars in the open cluster M 11 region. The accuracy of our sample is relative high, the average being some 1.1 mas/yr and 85 of the data better than 1 mas/yr.
Using an improved method, we finish the membership determination of 785 stars within the central 25' region of M 11 and membership probabilities for individual stars are given. The results are significantly good. The sample is very useful for further astrophysical researches of M 11. Some comparisons between our method and the old one are made, showing that the improved method is much better than the old method.
During the membership determination, we find that there exist both space- and velocity-mass segregation effects for M 11. This conclusion is also supported by other authors. A brief explanation is presented in the paper.
This work is partly supported by the National Natural Sciences Foundation of China (NSFC Grant No. 19603003). We are most grateful to the referee, Dr. B.J. McNamara, for useful suggestions for the paper.