An apparatus (40, 50) for signal bandwidth compensation, comprising: a digital predistortion filtering unit (401, 5011), a compensation filter (402, 502), a conversion unit (403, 503), and a power amplifier (404, 504); wherein the digital predistortion filtering unit (401, 5011) is configured to receive an original signal, perform predistortion processing on the original signal, and output a predistortion signal to the compensation filter; the compensation filter (402, 502) is configured to receive the predistortion signal from the digital predistortion filtering unit (401, 5011), compensate for distortion caused during a process of transmitting the predistortion signal to the power amplifier, and output a compensated predistortion signal to the conversion unit (403, 503); the conversion unit (403, 503) is configured to receive the compensated predistortion signal from the compensation filter (402, 502), convert the compensated predistortion signal into an analog signal, perform frequency mixing processing, and output a predistortion signal experiencing the frequency mixing to the power amplifier (404, 504); the power amplifier (404, 504) is configured to receive the predistortion signal experiencing the frequency mixing from the conversion unit (403, 503), amplify the predistortion signal experiencing the frequency mixing, and output an amplified signal; wherein a parameter of the compensation filter (402, 502) is obtained by using the following formula: w = x ′ ⋅ x − 1 ⋅ x ′ ⋅ q; wherein, w is a parameter matrix of the compensation filter, w = [ w -N, w -N +1,......, w N] T, and an order of w is 2 N + 1; q is a first parameter matrix, q = [ q -M, q -M +1,....., q M] T, an order of q is 2 M + 1, and the first parameter matrix is a parameter matrix with the least number of columns that is obtained according to a target performance index of the apparatus, wherein the target performance index is a performance index, which needs to be reached after the compensation filter (402, 502) performs compensation for the conversion unit (403, 503); x is a second parameter matrix, x = x − M − N, x − M − N + 1,......, x − M + N x − M − N + 1, x − M − N + 2,......, x − M + N + 1,...... x M − N, x M − N + 1,......, x M + N,, the second parameter matrix is obtained by transformation by a transformation matrix, the transformation matrix is a matrix obtained by performing a convolution operation according to a parameter matrix of a filter feature of a device in the conversion unit, and an order of the transformation matrix is 2 M + 2 N + 1; and x' is a conjugate transpose matrix of x. w is a parameter matrix of the compensation filter, w = [ w -N, w -N +1,......, w N] T, and an order of w is 2 N + 1; q is a first parameter matrix, q = [ q -M, q -M +1,....., q M] T, an order of q is 2 M + 1, and the first parameter matrix is a parameter matrix with the least number of columns that is obtained according to a target performance index of the apparatus, wherein the target performance index is a performance index, which needs to be reached after the compensation filter (402, 502) performs compensation for the conversion unit (403, 503); x is a second parameter matrix, x = x − M − N, x − M − N + 1,......, x − M + N x − M − N + 1, x − M − N + 2,......, x − M + N + 1,...... x M − N, x M − N + 1,......, x M + N,, the second parameter matrix is obtained by transformation by a transformation matrix, the transformation matrix is a matrix obtained by performing a convolution operation according to a parameter matrix of a filter feature of a device in the conversion unit, and an order of the transformation matrix is 2 M + 2 N + 1; and x' is a conjugate transpose matrix of x.