A method for manufacturing a needle walls assembly of a circular knitting machine comprising: a) providing a needle bed body and insertion sheets, wherein the needle bed body is provided with slots, the needle bed body is introduced with a heat treatment deformation coefficient to keep a first datum plane for knitting needles and a second datum plane for needle walls, bottoms of the slots are milled to exceed a range of the heat treatment deformation, each of the insertion sheets has a first portion at a front end thereof, a second portion at a rear end thereof and a third portion between the first portion and the second portion, the first portion and the second portion correspond to the first datum plane and the second datum plane, respectively, and a non-grinding accuracy and an external size of the first portion and the second portion of each insertion sheet are controlled within a tolerance range; b) measuring sizes of the inserting sheets and the bottoms of the slots; c) milling each slot when the size of the bottom of the slot measured in step b) is below a first standard, so that a gap is formed between the third portion of the insertion sheet and the bottom of the slot to prevent the third portions from touching the bottoms of the slots; d) after heat treatment, measuring sizes of the first datum plane and second datum plane; e) machining the first datum plane and second datum plane when the sizes measured in step d) do not meet a second standard; and f) inserting the insertion sheets into the slots one by one with making the first portion and the second portion closely attached on the first datum plane and second datum plane, respectively. a) providing a needle bed body and insertion sheets, wherein the needle bed body is provided with slots, the needle bed body is introduced with a heat treatment deformation coefficient to keep a first datum plane for knitting needles and a second datum plane for needle walls, bottoms of the slots are milled to exceed a range of the heat treatment deformation, each of the insertion sheets has a first portion at a front end thereof, a second portion at a rear end thereof and a third portion between the first portion and the second portion, the first portion and the second portion correspond to the first datum plane and the second datum plane, respectively, and a non-grinding accuracy and an external size of the first portion and the second portion of each insertion sheet are controlled within a tolerance range; b) measuring sizes of the inserting sheets and the bottoms of the slots; c) milling each slot when the size of the bottom of the slot measured in step b) is below a first standard, so that a gap is formed between the third portion of the insertion sheet and the bottom of the slot to prevent the third portions from touching the bottoms of the slots; d) after heat treatment, measuring sizes of the first datum plane and second datum plane; e) machining the first datum plane and second datum plane when the sizes measured in step d) do not meet a second standard; and f) inserting the insertion sheets into the slots one by one with making the first portion and the second portion closely attached on the first datum plane and second datum plane, respectively.