IWorkspaceFactory workspaceFact = new RasterWorkspaceFactoryClass();
            IRasterWorkspace2 rasterwr = (IRasterWorkspace2)workspaceFact.OpenFromFile("E:\\delete\\xuanzhi\\grid", 0);
            IRasterDataset rasterdataset = rasterwr.OpenRasterDataset("tingrid");
            IRasterBandCollection rasterbands = (IRasterBandCollection)rasterdataset;
            IRasterBand rasterband = rasterbands.Item(0);
            IRawPixels rawpixels = (IRawPixels)rasterbands.Item(0);
            IRasterProps rasterpro = (IRasterProps)rasterband;
           

            IRasterDataset2 rasterDataset2 = (IRasterDataset2)rasterdataset;
            IRaster raster = rasterDataset2.CreateFullRaster();

            IRaster2 raster2 = (IRaster2)raster;

            IPnt pBlockSize = new PntClass();
            IEnvelope envelope = rasterpro.Extent;
            pBlockSize.SetCoords(envelope.Width,envelope.Height);

            IPixelBlock pixelBlock = raster2.CreateCursorEx(pBlockSize).PixelBlock;
            int w = pixelBlock.Width;
            int h = pixelBlock.Height;
            //read the first pixel block
            IPnt topleftCorner = new PntClass();
            topleftCorner.SetCoords(0, 0);
            raster.Read(topleftCorner, pixelBlock);
            //modify one pixel value at location (assume the raster has a pixel type of uchar)
            IPixelBlock3 pixelBlock3 = (IPixelBlock3)pixelBlock;
            System.Array pixels = (System.Array)pixelBlock3.get_PixelData(0);

            for (int i = 0; i <w; i++)
                for (int j = 0; j <h; j++)
                    if (i == j)
            pixels.SetValue(Convert.ToByte(100),i,j);

            pixelBlock3.set_PixelData(0,(System.Object)pixels);
            //write the modified pixel block to the raster dataset
            IRasterEdit rasterEdit = (IRasterEdit)raster;
            rasterEdit.Write(topleftCorner, pixelBlock);