The utility model discloses a fixing structure with an inner pipe on a shell of an engine oil liquid level measuring sensor. The heat exchanger comprises a shell and an inner pipe, ribs for welding are designed at the inner bottom of the shell, a welding face corresponding to the shell 1 is arranged on the inner pipe, the inner pipe is inserted and assembled at the bottom of the shell in advance,and the ribs of the shell are welded and melted on the welding face of the inner pipe, so that the inner pipe and the shell are fixed together in a sealed mode. A plurality of ribs for welding are arranged at the inner bottom of the outer shell, the ribs are melted on the welding face of the inner pipe after ultrasonic welding, the inner pipe and the outer shell are sealed together, a sealing ringis not needed, long-term sealing is firm, cost is low, and the assembling process is simple.