There is the presentation of experimental results of surfase canal resistance value effect on electrical and photoelectrical characteristics of large square p-i-n-photodiodes with guard ring, fabricated from p-type silicon with specific resistance 20~kOhm*sm. The authors investigated and made analysis of the effect of canal resistance on both, photosensitive squares and quard ring dark currents, and, photoelectric correlation coefficient and watt-ampere characteristics, for extensive range of values. Authors found the optimal mean of surface canal resistance for p-i-n-photodiodes and stand the requirements to its value on different parts of the surface topological picture, if it would be nesessary for improvement of devices`s characteristics.