High-velocity oxygen-fuel (HVOF) sprayed WC-12Co coating can improve system hardness and wear-resistance significantly. However, the coating would suffer decarburization phenomenon due to the high spray temperature and the large cooling rate in the HVOF process. With the application prospect of introducing thick WC-12Co coating into some heavy-load rolling pairs to improve tribological performance and wear-resistance, such as the rolling bearing for thrust vector control in solid rocket engine, this study adopts low-temperature high-velocity liquid fuel spray process to fabricate thick coatings on bearing steel. The modified process with a spray temperature of around 1700 K is realized by the replacement of oxygen by oxygen-nitrogen mixed gas and the introduction of water-cooling system. Phase distribution, elementary composition, microstructure, bonding strength, elastic modulus and microhardness of coatings are investigated to verify the feasibility and advantage of the process. The bonding mechanism between the coating and the substrate is clarified. Based on experimental data and the assumption of WC skeleton structure filled up with cobalt phase, a simple formula of the microhardness of WC-12Co coating is proposed for theoretical predication and coating design.