The utility model relates to a mechanical downhole switch used for oil field well test production testing. An outer cylinder (11) is connected with the position between an upper and a lower single flow valves (3, 16) through a joint (8), and the joint (8) is connected with an inner cylinder (10) which extends to the lower single flow valve (16) in the outer cylinder (11). The tail end of the inner cylinder (10) is connected with a desilting cylinder (13) of which the tail end is provided with a plug (14). The upper part of the inner cylinder (10) is lined with a sliding bush (9), and preload spring columns (12) are arranged between the sliding bush (9) and both end surfaces of the desilting cylinder (13). Sealing glands are arranged among the joint (8), the outer cylinder (11) and the inner cylinder (10) and between the inner cylinder (10) and the sliding bush (9). A flow guiding ring cavity (19) which is communicated with the inner cavity of the lower single flow valve (16) is formed between the outer and the inner cylinders (11, 10), and the ring cavity is communicated with the inner cavity through a side hole (20) on the inner cylinder (10). In the process of implementing downhole switching, the procedure is easy. The switching action can be accomplished in a short time only falling or lifting a down-hole pumping rod.