There is often time/cost pressure for well testing operations to be conducted in the shortest time frame, meaning that testing operations may be terminated early, before pressure transient testing has been fully utilized to investigate the reservoir. In the past cable line was mostly used for this purpose, but its installation process and weak adaptability made it less popular. Low frequency electromagnetic wave (EM) could be used in long distance downhole communication. In this paper the attenuation mechanism of EM was studied, tools were prepared which integrated pressure sensor with EM modulator, finally field trial in the shale oil well in Xinjiang oilfield was attempted to verify this approach. A downhole-to-surface communication model consisting of wellbore structure (the stem) and an isolated downhole in-line cylinder (the electrode) embedded in the earth was considered. EM signal was applied on the tubing positioned at the bottom of wellbore, and the received signal was picked up at the surface between the two ground points. The analysis included consideration of casing longitudinal and surface impedance, joint resistance, voltage source resistance, and earth propagation effects to provide a realistic model for assessing the performance of the communication channel. Field trials in the oil well was also launched to verify the model. The results demonstrated that internal impedance, external inductance, interface impedance of casing and propagation effects in the formation were the most influential factors during the downhole EM communication, the model took into account those factors and quantified the wellbore impedance. The metallic structure of wellbore was used as the conduit along which to transmit EM signals, the electric resistivity of subsurface formation played a vital role as the signal travelled up to the surface, generally lower resistivity led to higher leakage of energy into the reservoir and an average of 10Ω.m formation would limit the communication distance within about 1000 m according to the theoretical calculation. The tool comprised pressure senor and EM modulator, pressure data was modulated with 5 Hz EM wave through frequency-shift keying and the signal was amplified by metal coils, 50 Hz noise was filtered through wavelet algorism. The tool was tripped into the oil well to the depth of 1466 m and the pressure signal was received and decoded in a real time manner on the ground. The intensity of signal dropped as the tool went down, it attenuated much heavier during the low electric resistivity zone, testifying the mechanism study. Due to the installation of the EM device, the stroke of rod pump could be adjusted based on accurate liquid level information. This paper described the engineering concepts underlying the model and how it improved downhole EM communication technology. It also documented testing and summarized actual field results of oil well successfully in highly resistive and attenuated formations guided by the calculation results of model.