The invention discloses a pressure equalizing chamber, a mounting method thereof and a three-dimension space multi-point pressure measuring and cross section type gas flow measuring device containing the pressure equalizing chamber. The pressure equalizing chamber is of an isosceles triangle thin wall cavity structure, two waist edges of an isosceles triangle are each continuously provided with one or more pressure measuring openings, and all the pressure measuring openings are communicated with a thin wall cavity. By the adoption of the three-dimension space multi-point pressure measuring and cross section type gas flow measuring device, multiple pressure measuring points are arranged at different streamline positions in a three-dimension space, and due to the fact that the pressure measuring cross section exceeds the pressure measuring cross section designed by any existing measuring technology, the pressure equalizing chamber, the mounting method thereof and the three-dimension space multi-point pressure measuring and cross section type gas flow measuring device are particularly applicable to the occasion that the flow speed of a large pipe is unevenly distributed; besides, due to the special thin wall cavity structure of the pressure equalizing chamber, ash accumulation does not occur easily, ash removing needle design is further adopted, and the ash accumulation tendency is reduced to the maximum degree; the gas flow measuring device has the remarkable advantages of being resistant to blocking, resistant to wearing, resistant to high temperature, high in measuring accuracy, stable in measurement value and the like.