A method for detecting a Direction of Arrival, DOA, of an echo in a Synthetic the Aperture Radar, SAR, comprising the steps of: performing range pulse compression on echo data obtained by each channel of the SAR in elevation to obtain a compressed SAR signal; performing Fourier transform on the compressed SAR signal along the channel on each range gate; interpolating a result obtained after the Fourier transform with a frequency-domain interpolation algorithm; acquiring a frequency at an amplitude maximum in a frequency domain after the interpolation; and acquiring the DOA according to the frequency, wherein the compressed SAR signal is ĝ n ( τ, t), with g ⁀ n τ t = σ p r t − t 0 exp − j 4 π λ R T τ exp j 2 π λ d n sin α t 0, wherein τ is an azimuth slow time; t is a range fast time; σ is a backscattering coefficient of a target; p r ( t-t 0) is a point target SAR signal envelope after pulse compression; t 0 is a two-way delay of the echo; R T ( τ) is an instantaneous slant range from a transmitter to the target; α ( t 0) is the off-boresight angle of the DOA; d n is a position of an nth receiver with respect to the transmitter, an absolute value of d n being equal to a distance between the nth receiver and the transmitter; λ is a wavelength of the echo, wherein the step of performing Fourier transform on the compressed SAR signal along the channel on each range gate comprises: deleting, on a fixed range gate, a common term of channels of the SAR to obtain an N-dimensional vector v ( n), with ν n = exp j 2 π λ d n sin α t 0; and transforming the v ( n) into the frequency domain to obtain the result Γ( ξ), with Γ ξ = ∫ 0 L E exp j 2 π sin α t 0 λ d n exp − j 2 πξ d n d d n = sin c L E ξ − sin α t 0 λ exp − jπξ L E, wherein L E is an azimuth antenna length; ξ is a frequency-domain parameter, wherein the step of acquiring the DOA according to the frequency is: acquiring the off-boresight angle α ( t 0), with α ( t 0)= arc sin( λξ max), wherein ξ max is the frequency at the amplitude maximum in the frequency domain after the interpolation. performing range pulse compression on echo data obtained by each channel of the SAR in elevation to obtain a compressed SAR signal; performing Fourier transform on the compressed SAR signal along the channel on each range gate; interpolating a result obtained after the Fourier transform with a frequency-domain interpolation algorithm; acquiring a frequency at an amplitude maximum in a frequency domain after the interpolation; and acquiring the DOA according to the frequency, wherein the compressed SAR signal is ĝ n ( τ, t), with g ⁀ n τ t = σ p r t − t 0 exp − j 4 π λ R T τ exp j 2 π λ d n sin α t 0, wherein τ is an azimuth slow time; t is a range fast time; σ is a backscattering coefficient of a target; p r ( t-t 0) is a point target SAR signal envelope after pulse compression; t 0 is a two-way delay of the echo; R T ( τ) is an instantaneous slant range from a transmitter to the target; α ( t 0) is the off-boresight angle of the DOA; d n is a position of an nth receiver with respect to the transmitter, an absolute value of d n being equal to a distance between the nth receiver and the transmitter; λ is a wavelength of the echo, wherein the step of performing Fourier transform on the compressed SAR signal along the channel on each range gate comprises: deleting, on a fixed range gate, a common term of channels of the SAR to obtain an N-dimensional vector v ( n), with ν n = exp j 2 π λ d n sin α t 0; and transforming the v ( n) into the frequency domain to obtain the result Γ( ξ), with Γ ξ = ∫ 0 L E exp j 2 π sin α t 0 λ d n exp − j 2 πξ d n d d n = sin c L E ξ − sin α t 0 λ exp − jπξ L E, wherein L E is an azimuth antenna length; ξ is a frequency-domain parameter, wherein the step of acquiring the DOA according to the frequency is: acquiring the off-boresight angle α ( t 0), with α ( t 0)= arc sin( λξ max), wherein ξ max is the frequency at the amplitude maximum in the frequency domain after the interpolation. deleting, on a fixed range gate, a common term of channels of the SAR to obtain an N-dimensional vector v ( n), with ν n = exp j 2 π λ d n sin α t 0; and transforming the v ( n) into the frequency domain to obtain the result Γ( ξ), with Γ ξ = ∫ 0 L E exp j 2 π sin α t 0 λ d n exp − j 2 πξ d n d d n = sin c L E ξ − sin α t 0 λ exp − jπξ L E, wherein L E is an azimuth antenna length; ξ is a frequency-domain parameter, wherein the step of acquiring the DOA according to the frequency is: acquiring the off-boresight angle α ( t 0), with α ( t 0)= arc sin( λξ max), wherein ξ max is the frequency at the amplitude maximum in the frequency domain after the interpolation. acquiring the off-boresight angle α ( t 0), with α ( t 0)= arc sin( λξ max), wherein ξ max is the frequency at the amplitude maximum in the frequency domain after the interpolation.