Question

Model.getSelectionModel().selectRow(0) not work …

Answer 1

this.store = new Ext.data.Store({
    ...
    listeners: {
        load: function() {
            this.grid.getSelectionModel().selectFirstRow();
        },
        scope: this
    }
});

this.grid = new Ext.grid.GridPanel({
    ...
    store: this.store
});

Something like this should work, assuming this.store and this.grid exist, I’m sure you can adapt it.