Abstract: The focus of the ecological problems in Tarim River is contabescence of natural vegetation and desertificaTtion at the lower reaches because of water shortage-. It is the key to estimate the economical loss of ecological resources quantificationally, and make the principle to calculate ecological economy. It becomes important to esti mate the economical loss and the cost for the comeback of natural ecosysltem, and comparea wiIn lne Deitean s olthe economical increasing at the upper reaches. Since 1949, irrigated area in the triDutarles o ar 10'tem n inexpanded for 42.65×10'hm², oases area there is 160×10'hm³ now; and it has increased to 3.85×10'hm² in the trunk stream from zero in 1949. Annual runoff from tributaries to the trunk has reduced for 25×108~30 X 10 m³ in last 50 years, 74.2% of the river water consumed in the tributaries. Runoff in the trunk stream decreased gradully because of the increasing of drawn water for irrigation in the tributaries ; and runoff at the low-er reaches of Tarim River reduced greatly since the percent of water consuming in the upper and middle reacheshas increased. The benefit of water usage is different in various place, various periods or for various purpose. Even in the same place or same period, economical benefits of water usage will be varied if use mode is dfferent. The efficiency of water utilization in'Tarim watershed is quite lower and water used for irrigation is more than 95% of the drown water from river in the tributaries. Based on the value theory of water resources and usagesituation of river water in Tarim watershed, benefit apportion can be used to calculate the average benefit water usage for agriculture. If the apportion coefficient is 0.b 5, beneit of per ubic me er waLer wli be o drn n farwhen water used to irrigation in the tributaries of 'Tarim liver. 1 E 0.0000 v m o Rver wanenoff aot the lonwerirrigation there every year that makes 40×10° Yuan of direct benefit in agriculture. Annual runoff at the lower reaches has reduced for 70% compared to that 30 years ago- If the annual runoff in the lower increase to 9. 0 X 10 8 m³/a which equals the average in 1966~1975, 8×10°m³ more of runoff should be flow from the tributaries to the trunk stream every year, and the bank for control flood should be built along the main reach of 'Tarim Riv-er. The total cost of increasing runoff from the tributaries and bank building will be 8. 8×103 Yuan.

Key words: Tarim River, water resources, benefit of water usage, ecological loss