Taking small watershed as a unit

acxeording to the allocating feature of mountainous protection forest system

and adopting locating and semi-locating research technique

the function of water accumulation and soil conservation of mountainous protection forest system was monitor

d and analyzed in hierarchical way. The research results are as follows. The difference of soil and water conserative effectis relatively large in different land types

different land use methods and different forest types. The main source of sand producing is the bare area of central Guizhou plateau and cultivated slopeland in drainage area

The erosion quantity of cropland is 18.7-36.0 times than that of forest land; The erosion quantity of bare land is far larger than that of cultivated slopeland

and is as high as about 100 times than that of forest land. After the protection forest system was established

the protection effect was obvious

the mlulus of soil erosion reduced following the increase of forest cover rate The modulus of soil erosion decreased 36% when the forest cover rate of drainage area increased from 18.6% to 42.4%.After the construction of plantation in sloping field

the surfac

mnoff decreased from 79.4% to 96.9%，and the silt amount d

creas

d from 87.8% to 99.9%;In order to control soil and w ester loss of small westershed in mountainous region

forest cover rate must be more than 30%.