This paper presents a calibration scheme for delay mismatch between envelope and phase in the OFDM polar transmitter. An asynchronous delay detection method is proposed to avoid using a complicated signal processing algorithm or synchronous elements which need high clocking rates for detecting small delay mismatch. This scheme uses buffer delay chains to estimate the mismatch and then the estimated delay values are asynchronously stored in registers. It is verified that the proposed scheme well suites application to the OFDM polar transmitter through SPW, Matlab and HDL simulations. It achieves the margin of about 20 dB at 20 MHz offset, 10 dB at 40 MHz offset in terms of spectral limit specified in WLAN standard.