The invention discloses a pre-combustion chamber structure of a fuel gas engine. The pre-combustion chamber structure of the fuel gas engine comprises a high-voltage guide wire sleeve, a pre-combustion chamber body, a spark plug, a one-way valve and a spray nozzle, wherein the lower end of the pre-combustion chamber body is provided with a pre-combustion chamber upper cavity; a spark plug mountinghole is formed in one side above the pre-combustion chamber upper cavity; a one-way valve mounting hole is formed in the other side above the pre-combustion chamber; the one-way valve mounting hole communicates with the pre-combustion chamber upper cavity through a gas inlet channel; the high-voltage guide wire sleeve is fixedly arranged at the upper end of the pre-combustion chamber body; the upper end of the spray nozzle is provided with a pre-combustion chamber lower cavity; the spray nozzle is arranged at the lower end of the pre-combustion chamber body; the pre-combustion chamber lower cavity and the pre-combustion chamber upper cavity of the pre-combustion chamber body define a pre-combustion chamber cavity; and the lower end of the spray nozzle is provided with a spray channel which communicates with the pre-combustion chamber lower cavity. The pre-combustion chamber structure of the fuel gas engine forms relatively great ignition energy through combustion of a high-concentration natural air mixture to ignite the relatively thin gas mixture in a primary combustion chamber, so that the purpose of improving power and heating efficiency of the whole machine is achieved.