A two-dimensional mathematical model was developed for predicting the performance of an open-type water-cooled fiat-plate solar collector, and solved numerically through an that there is an optimum length and tilt angle for the absorbing plate for which the implicit finite difference method. The effects of various environmental and geometric conditions on energy absorption for the collector were investigated. The results predict collector could obtain the highest solar energy absorptance. The latent heat pur of water evaporation can be 3 to 15 times larger than the sensible heat flux under normal operating conditions. The wind speed and the inlet water temperature have a large influence on the energy absorption of the collector The effects of the solar incident flux, the atmospheric humidity and temperature, the absorbing plate tilt angle and length, and the water film thickness on the temperature rise of the water film and/or the absorptance of the collector are clarified. The open-type flat-plate collector is suitable to operate at lower inlet water temperatures and in regions where the local latitude is in the range of 20 degreesN-40 degreesN, and the weather is humid and hot with low winds. [S0199-6231(00)00202-1].