The invention discloses lead-free solder and a preparation method thereof. The lead-free solder comprises a lead-free solder matrix and a reinforced phase, and the reinforced phase accounts for 0.1%-1% of the lead-free solder matrix by mass. The lead-free solder matrix is one of a Sn-Ag-Cu alloy, a Sn-Sb alloy, a Sn-In alloy, a Sn-Cu alloy and a Sn-Ag alloy. The reinforced phase is a material of two-dimensional transition metal carbide or carbonitride (MXene). The preparation method for the lead-free solder comprises the following steps that the MXene is placed in absolute ethyl alcohol, dispersed through ultrasonic oscillation and then uniformly mixed with the lead-free solder matrix in a certain proportion to be pressed into a green body; and finally sintering is conducted under protection of inert atmosphere, and the novel solder with higher mechanical, electrical and thermal properties than existing lead-free solder is prepared. The method is environmentally friendly and conforms to the development tendency of the modern electronic industry.