The invention provides a desulfurization agent for removing thiophenic compounds in oil products, and provides a preparation method of the desulfurization agent. Aiming at removal request of thiophenic sulfide in the oil products, desulfurization of the oil products can be realized by condensation reaction of thiophene and formaldehyde. Aiming at the low heterogeneous reaction efficiency problem caused by direct use of the formaldehyde and a liquid acid catalyst, desulfurization can be realized by mixing paraformaldehyde and cosolvent methanol or acetone with the liquid acid catalyst to form a desulfurization agent with good oil solubility to add into the oil products for reaction. The prepared liquid desulfurization agent has good oil solubility, and can form a homogeneous mixture by adding into the oil products, so that the desulfurization efficiency can be effectively improved.