S Situ or small lake has many function which among other things, as a medium to rain fall reiceptacle (Nature reservoir). From 1940 to 1994 situs in Jabodetabek had apparently decreased both quantity and totally extent. One of the major problem that caused of those decreasing is shallowing process of situ’s water. That process caused by increasing of accumulation sedimen on the bottom of situ. Hence it is Immensely required some efforts to conservate situ with considering the shallowing problem. All situs in Cibinong region towards on Bogor have more function where in able to be such a deep well. Meanwhile, Cibinong which known as water penetration area has been available several situs, one of them is Situ Cibuntu, that has 15, 295.350 m2 extent and 13,544.950 m3 capacity.The great contribution of sediment to enter the situ where comes from the land and farm on the area around the river flood, and that usually called watershed. Where in that process could be happen as a run off, erotion and also scouring. That sedimen are transferred as suspension particulate is the flowing of waters body, and that stated as suspended solid. Disclosing the relation between sediment phenomenon and the shallowing problem, in this instance is applied the mathematic model of sedimen mass balance that could explaining the balance of sedimens load in the waters body of situ. The basic idea of that model it’s from the model box. In model box, situ is imaginated as a box where in sedimens load in situ is obtained as a difference between sedimen load from inlet, outlet and deposit to the bottom of situ. The estimation process is basaed on the method of Runge Kutta with computer application of Powersim version 2.0. This research itself hada been done for 81 days and required field data such as flow rate, TSS (Total Suspended Solid) consentration in inlet and waters body of situ, density of sedimen, and also the average thickness of sedimen layer on the bottom of situ whwn it look before the research started.